JPH10107563A - Analog switch circuit and photoreceiver / amplifier using the same - Google Patents

Abstract

(57) [Summary] To provide an inexpensive analog switch circuit which is versatile and operates with high accuracy in a wide frequency band. SOLUTION: A light receiving and amplifying device having a photodiode PDi and an amplifier APi for converting a light receiving current from the photodiode PDi into a voltage and amplifying the voltage. Two resistors R ₁ and R 2 connected in series with each other between the output 2 of the amplifier APi and the ground V _EE
2 and two junction type FETs JF ₁ and JF ₂ each having a source S connected to a connection point between these resistors and an output 2 of the amplifier APi, and a drain D connected to a common output terminal 3. An analog switch circuit 1 comprising a control circuit 5 for outputting a control signal for turning on / off each of the junction type FETs JF ₁ and JF ₂ is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog switch circuit used for switching a gain of a pickup section of a digital video disk player or the like, or an electronic volume of a digital audio device such as a mini disk player or a multiplayer.

[0002]

2. Description of the Related Art Conventionally, as an analog switch circuit used for an electronic volume of a digital audio device,
For example, the one shown in FIG. 9 is known. The analog switch circuit connects four resistors R ₁ to R ₄ in series with each other between the ground and the input terminal 51 for receiving a digital audio signal, each emitter to the junction of these resistors interacts with the said input terminal 51 Connect each collector to amplifier 5
2 input terminals and four transistors Tr _{1 to} Tr ₄
And an ON control signal is sent from the control circuit 53 only to the base of the transistor in accordance with the command signal from the input terminal 53a, thereby turning on the transistor. The resistance values of the _four resistors R _{1 to} R ₄ are selected such that the attenuation increases by a constant decibel as they are connected in series. Therefore, the input digital audio signal is input to the amplifier 52 through the resistance of the input terminal 51 side from the conducting transistor in order, and is amplified at a constant rate. Are conducted, the lower the level of the digital audio signal is output.

However, in the analog switch circuit shown in FIG. 9, a bipolar transistor T is used as a switching element.
because of the use of r ₁ to Tr _4, the influence of the base current flowing through the base when the transistor is conductive, the input terminal 5
The input signal from 1 is attenuated by 1 / h _FE (= current amplification factor of a transistor with a common emitter), and an accurate signal attenuation cannot be obtained. Therefore, this analog switch circuit is not suitable for an electronic volume of a digital audio device that requires an accurate attenuation. In addition, since bipolar transistors Tr _{1 to} Tr ₄ cannot flow current from the collector to the emitter, they cannot be used as switching elements of a circuit that needs to flow current in both directions, and lack versatility.

Here, if a C (Complementary) -MOS transistor, which is a unipolar transistor, is used as a switching element, the input impedance of the gate is very high and the gate current hardly flows, so that an accurate attenuation can be obtained. In addition, current can flow in both directions, and the above-mentioned disadvantages are eliminated. However, C-MO
The S transistor is, as compared with the bipolar transistor,
Since the operating frequency band is narrow and the accuracy is deteriorated due to the offset, if an analog switch circuit is configured using all the switching elements as C-MOS transistors, an amplifier operating at a high speed or a high frequency band is connected to the input / output of this circuit. There is a problem that it is difficult to do. Therefore, in order to realize an analog switch circuit that operates accurately over a wide frequency band and has excellent versatility, it is necessary to simultaneously form a bipolar transistor and a C-MOS transistor on one semiconductor substrate by an integrated circuit process. Is required.

On the other hand, as a conventional optical amplifying device used for a pickup of a digital video disk player or the like, for example, one shown in FIG. 10 is known. This optical amplifying device has six photodiodes PD _{1 to} PD whose anode is grounded to GND and receives reflected light from the magneto-optical disk.
And D _6, the inverting input terminal to the cathode side of each photodiode is connected, the non-inverting input terminal and the six amplifiers AP ₁ ~AP ₆ which is connected to a common intermediate potential Vs, the inverting of each amplifier AP ₁ ~AP ₆ Feedback resistor R ₁ or R ₂ connected between input and output terminals
And the power supply voltage Vcc. FIG. 11 corresponds to 1 in FIG.
FIG. 4 is a detailed circuit diagram showing a pair of photodiodes PDi and amplifiers APi extracted therefrom. The amplifiers APi each include a current-voltage conversion differential amplifier circuit 55 that converts a light receiving current signal from the photodiodes PDi into a voltage signal, It comprises a phase compensation circuit 56 for performing compensation, an output circuit 57 for amplifying a signal by a push-pull method, and a control signal input terminal 58 for inputting a signal for activating or deactivating the amplifier APi. Thus, according to the information recorded on the magneto-optical disk, the photodiode
The light receiving current output from PDi is converted into a voltage by the amplifier APi, amplified, and output from the output terminal 59 as a voltage signal Vi.

The optical amplifying device (FIG. 10) performs signal processing such as calculation based on a difference between _four voltage signals V _{1 to} V ₄ of the six output voltage signals by a signal processing unit (not shown). The signal recorded on the surface of the magneto-optical disk is reproduced, and the remaining two voltage signals V ₅ and V ₆ are used for positioning the incident light. By the way, recent magneto-optical disks include:
Some discs have digital signals recorded in two layers on one side of the disc. In such a two-layer disc, the amount of reflected laser light differs between the first layer and the second layer. Therefore, high S
In order to accurately read a signal while securing a / N ratio and a wide frequency band, when the irradiation laser is set to a constant power, the voltage change amount with respect to the incident light amount on the light receiving device side is changed to the first layer and the second layer.
It is necessary to switch between layers to make the level of the output signal from the light receiving device constant.

However, in the above-mentioned optical amplifying device, the switching circuit for switching the amount of voltage change between the first layer and the second layer is not provided around the amplifier APi as shown in FIG.
The amplifier APi shown in FIG.
And does not have a built-in switching circuit to switch the gain. Therefore, in order to obtain an optical amplifier having excellent versatility by operating accurately over a wide frequency band corresponding to a two-layer type disc, the same reason as described in the analog switch circuit for the electronic volume in FIG. Therefore, it is essential to add an analog switch circuit in which a bipolar transistor and a C-MOS transistor are formed together on one semiconductor substrate to the amplifier APi.

[0008]

An integrated circuit process which is used for gain switching and electronic volume control of digital equipment and is indispensable for a versatile analog switch circuit which operates accurately over a wide frequency band, that is, a bipolar transistor. The method for forming the C-MOS transistor and the C-MOS transistor on one semiconductor substrate is as shown in FIG.
That is, in this manufacturing method, in step S1, a surface oxide film of a P-type semiconductor substrate is patterned and then an N-type element is thermally diffused to form an N ⁺ buried layer. In step S2, the surface oxide film is entirely stripped. Then, an N layer is grown by vapor phase epitaxy, and in step S3, an oxide film on the surface of the N layer is patterned, and a P-type element is thermally diffused from the silicate glass formed thereon to the N layer. Bipolar region and C-MO
The S region is separated, and in step S4, an N ⁺ cc band connecting the N ⁺ layer of step S1 to the surface through the N layer is formed by diffusion of an N-type element (collector compensation diffusion). Next, in step S5, a P-type element is thermally diffused into a predetermined portion of the C-MOS region to form a P-well, and in step S6, a bipolar transistor is formed.
Oxide film formation and patterning of the P-type element and the N-type element in both regions of the C-MOS are performed, and the surface inversion voltage is determined in step S7 by field-doping the portion other than the channel region in step S7. The gate portion is exposed to a high-temperature oxidizing atmosphere to form a local oxide film for separating the elements.

Further, in step S9, the channel portion of the C-MOS region is doped with boron to determine a threshold voltage. In step S10, boron is thermally diffused in the base portion of the bipolar region. A polysilicon electrode is formed on the gate in the MOS region. Next, step S12
And the emitter region in the bipolar region and the N-channel CM
The thermal diffusion of phosphorus into the source and drain regions of the OS
⁺ Layer is formed, and in step S13, a P-channel C-MOS
The boron source part and the drain part of the frequency band by thermally diffusing P ⁺
Form a layer. Finally, in step S14, an oxide film or a silicate glass film is opened in the contact portions of both the bipolar and the C-MOS. In step S15, wiring patterning is performed using aluminum or the like. In step S16, the surface is formed using silicate glass or the like. After covering with a protective film, a portion required for electrical connection is opened to complete a semiconductor substrate having both bipolar and C-MOS transistors.

However, in the above-mentioned conventional method for manufacturing a semiconductor substrate, both bipolar and C-MOS transistors having different structures are formed on one semiconductor substrate.
In addition to a process common to both transistors surrounded by a double rectangle, a process (steps S5, S9, S11, S13) unique to a C-MOS transistor surrounded by a double rectangle is required. Therefore, in order to operate with high accuracy in a wide frequency band with versatility, an analog switch circuit used for gain switching and electronic volume control of digital equipment,
If an attempt is made to make a single integrated circuit incorporating both bipolar and C-MOS transistors, a process unique to the above-described C-MOS will be required compared to the conventional example formed with an integrated circuit having only bipolar transistors as shown in FIG. There is a problem in that the number of steps increases, the number of manufacturing days increases, and the manufacturing cost increases.

Therefore, an object of the present invention is to apply the invention to versatility in gain switching and electronic volume control of digital equipment by using elements similar in operation but similar in manufacturing process to bipolar transistors instead of C-MOS transistors. An object of the present invention is to provide an analog switch circuit which can operate with high accuracy in a wide frequency band, can be manufactured quickly and inexpensively by reducing the number of manufacturing steps, and a light receiving and amplifying device using the same.

[0012]

According to a first aspect of the present invention, there is provided an analog switch circuit for attenuating an input signal according to ON / OFF of a plurality of junction FETs and outputting an output signal. And a control circuit that outputs a control signal for selecting and turning on and off the junction FET.

In the analog switch circuit of the first aspect, the control circuit outputs a control signal to a specific junction FET, and the specific junction FET is turned on / off by the control signal.
The input signal is attenuated according to the on / off state and output as an output signal. Here, the junction FET has a variation in the pinch-off voltage, but this problem can be solved by appropriately setting the power supply voltage according to the maximum amplitude of the input signal. Since almost no current flows, an accurate amount of attenuation can be obtained, and the current to be turned on and off can be flowed in both directions, which is versatile.
In addition, unlike the C-MOS transistor, the junction type FET can be manufactured in substantially the same manufacturing process as the bipolar transistor which is another component of the analog switch circuit, so that it can be manufactured quickly and inexpensively by reducing the number of manufacturing steps. . In other words, the analog switch circuit, which can be configured by integrating a junction type FET and a bipolar transistor on a single semiconductor substrate, can be widely applied to gain switching and electronic volume control of digital equipment, and operates with high accuracy in a wide frequency band. You do it.

According to a second aspect of the present invention, there is provided a light receiving and amplifying device having a photodiode and an amplifier for converting a light receiving current from the photodiode into a voltage and amplifying the voltage. A plurality of resistors connected in series with each other between the output and the ground, and a plurality of the above-mentioned plurality of sources each connected to a connection point of these resistors and the output of the amplifier, and a drain connected to a common output terminal. And a junction type FET.

According to a second aspect of the present invention, there is provided a light-receiving amplifying device for converting a light-receiving current from a photodiode into a voltage and amplifying the voltage, a voltage-dividing resistor including a resistor connected in series to the ground, And the output terminal and the common output terminal are connected by a plurality of junction-type FETs as switching elements to constitute an attenuation circuit of an analog switch circuit. Now, when a control signal is output from the control circuit of the analog switch circuit to a specific junction type FET of the above-described attenuation circuit, the junction type FET is turned on / off and changes to a specific voltage dividing resistance value, and the input signal is changed. The signal is attenuated by the amplifier at a ratio corresponding to the voltage dividing resistance value and output from the common output terminal. The analog switch circuit of this photoreceiver / amplifier is also a junction type F instead of a C-MOS transistor.
Since the ET is used, it can be integrated on a single semiconductor substrate together with the bipolar transistor, can be applied to the gain switching of the light receiving and amplifying device with versatility for the same reason as described in claim 1, and has a high accuracy in a wide frequency band. Works.

According to a third aspect of the present invention, there is provided a light receiving and amplifying device having a photodiode and an amplifier for converting a light receiving current from the photodiode into a voltage and amplifying the voltage. A resistor is connected between the output and the input, and the resistor and the junction FET are connected in series between the output and the input of the amplifier.

In the light receiving and amplifying device according to the third aspect, the specific junction type FE of the attenuation circuit is changed from the control circuit of the analog switch circuit.
When a control signal is output to T, the junction type FET is turned on and off, and a plurality of specific resistors are connected in parallel, and feedback corresponding to the combined resistance value is sent to an amplifier that amplifies the light receiving current from the photodiode. Join. Therefore, a signal amplified at a ratio corresponding to the combined resistance value is output from the amplifier of the light receiving amplifier. The analog switch circuit of this photoreceiver / amplifier is also a junction type F instead of a C-MOS transistor.
Since the ET is used, it can be applied to the gain switching of the light receiving and amplifying device with versatility for the same reason as described in claim 2, and operates with high accuracy in a wide frequency band.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is an equivalent circuit diagram of an analog switch circuit according to the present invention. This analog switch circuit 1 has two resistors R ₁ and R ₂ between an input terminal 2 receiving a digital signal and a ground (lowest potential) _VEE. Are connected in series,
An attenuating circuit 4 comprising two junction transistors represented as switching elements SW ₂ and SW ₁ between a connection point of the two resistors R ₁ and R ₂ and between the input terminal 2 and the common output terminal 3; And two terminals C ₁ , C 2 for outputting a control signal for turning on / off the switching elements SW ₁ , SW ₂ to the attenuation circuit 4.
It comprises a control circuit 5 represented as ₂ . And
Control circuit 5, so that an ON signal or only one of the terminals, the switching elements SW ₁ ON signal at the terminal C ₁
Is turned on, the digital signal input to the input terminal 2 is output from the output terminal 3 without being attenuated. On the other hand, when the switching element SW ₂ is turned on by the ON signal of the terminal C ₂ ,
The input digital signal is internally divided by the ratio of the resistance values to obtain R ₁ / (R
₁ + R ₂ ) and is output from the output terminal 3.

FIG. 2 shows a specific example of the above-described analog switch circuit 1. In this specific example, four series-connected resistors R ₁ having the illustrated resistance values are provided between the input terminal 2 and the ground _VEE. the to R ₄ is provided, a four-junction FETJF ₁ ~JF ₄ of P-channel type with a damping circuit 4 is provided between the connection point and the input terminal of each resistor each other and a common output terminal 3, the control circuit 5 From the four terminals C _{1 to} C _{4 as the} connection type F
To only one of ETJF ₁ ~JF ₄ so that outputs an ON signal. Resistance value of the four resistors, a single junction type FET which conducts with the changes from JF ₁ to JF ₄ in order, is determined as the attenuation factor of the attenuator circuit 4 increases by 2 db by partial pressure ratio I have.

The greatest feature of the analog switching circuit 1 is for the use of junction FETJF ₁ ~JF ₄ to the switching element. As described above, the junction type FET has an input impedance almost as high as that of a C-MOS transistor and hardly allows a gate current to flow, so that an accurate attenuation can be obtained and current can flow in both directions. Therefore, it can be applied to various circuits and is excellent in versatility. Also, junction type FET
As described with reference to FIG. 12, unlike the C-MOS transistor, it can be manufactured in substantially the same manufacturing process as the other bipolar transistors required for the analog switch circuit, so that the junction FET and the bipolar transistor are integrated on one semiconductor substrate. To reduce manufacturing man-hours (Step S5 in FIG. 12,
9, 11, 13), the analog switch circuit can be manufactured quickly and inexpensively.

FIG. 3 shows one junction type FET JFi (i = 1 to 4) of the analog switch circuit 1 of FIG.
FIG. 3 is an equivalent circuit diagram showing details of a control circuit 5 including i. In this equivalent circuit, a source S and a drain D are connected between a connection point Ji (input terminal 2 when i = 1) and an output terminal 3 of a resistor Ri (i = 1 to 4) on the input terminal 2 side. When the junction FET JFi is turned on by the ON signal (switch closed) from the terminal Ci and the junction FET JFi interposed therebetween, the gate voltage is set to the first voltage.
Power supply voltage Vcc ₁ and on-time voltage holding circuit 6 for holding the middle of the intermediate potential V _A of the ground potential V _EE, when terminal Ci is junction FETJFi is nonconductive the switch open, the gate voltage second power supply voltage A value lower than Vcc ₂ by the base-emitter voltage V _BE (for example, 0.7 V) of the transistor Q ₃ (Vcc ₂ −V
_BE ) and the off-state voltage holding circuit 7 and the junction type FETJ
The current control circuit 8 controls a current flowing from the gate G of Fi to the ground _VEE .

The on-time voltage holding circuit 6 is a junction type FE.
Connect the base B and collector C between the source S and the ground V _EE of TJFi, the PNP type which is interposed to connect the emitter E to the second power supply voltage Vcc ₂ and transistor Q _2, the transistor Q ₂ a diode D ₁ connected in forward direction between the gate G of the junction type FETJFi the emitter E. Also,
The off-state voltage holding circuit 7 has an emitter E connected to the second power supply voltage Vcc ₂ and a collector C connected to the gate G of the junction type FET JFi.
There the transistor Q ₃ of the PNP type which are respectively connected, comprising the transistor Q ₃ of the collector C and base B diode D ₂ connected toward the second power supply voltage Vcc ₂ respectively forward from, D ₃ Prefecture. Further, the current control circuit 8
The collector C is connected to the gate G of the junction type FET JFi and the ground V _EE
NPN transistor Q ₄ with emitters E connected to
With, (see FIG. 4) base B is diode D _4, through D _1, transistor Q ₅ of NPN type connected to the collector C of each said transistor Q ₄ collector C via the diode D ₁ (FIG. 4 a reference), the base B to the base B of the transistor Q ₄ is, the emitter E is respectively connected to the emitter E,
A switching transistor Q ₁ Tokyo to conduct the switch closed terminal Ci. The transistors Q ₄ and Q ₅
Form a current mirror circuit.

FIG. 4 shows a specific configuration and circuit constants of the equivalent circuit of FIG. 3, and the same members as those of FIG. 3 are denoted by the same reference numerals. In FIG. 4, replaced by a transistor Q ₉ terminals Ci of FIG. 3, the first power supply voltage Vcc ₁ and between the transistor Q ₁ and a second power supply Vcc ₂ and the transistor Q ₈ for on-off between the transistor Q ₂ and provided with a Q _10, it is provided transistors Q _6, Q ₇ between the transistor Q ₅ and the ground V _EE.

The analog switch circuit shown in FIGS. 3 and 4 operates as follows. Now, when the terminal Ci is switched off, the base B is set to “H” (V _EE +) when the first power supply voltage Vcc ₁ is applied.
(0.7 V or more), the transistor Q ₁ is turned on and the current I ₁
Flows, thereby turning on the transistor Q ₄ whose base B is common to Q ₁ (Q ₁ and Q ₄ are current mirror circuits), and when this is on, the current between C and E of the transistor Q ₄ is the same as I ₁ to flow only lowers the collector potential of the Q _4, D ₂ is turned off, D ₁ is turned on. Then, the on-time voltage holding circuit 6 operates to hold the gate voltage at the intermediate voltage _VA having the same potential as the source voltage. As a result, the gate-source voltage V _GS of the junction FET JFi becomes “L”. , The junction FET JFi is turned on. In this ON state, the input signal input to the connection point Ji is input not only to the source S of the junction FET JFi but also to the gate G, so that the gate-source voltage V _GS is independent of the amplitude of the input signal. However, the switching operation is maintained at a constant value, that is, at the intermediate potential _VA , and a stable switching operation is realized.

On the other hand, when the terminal Ci is switched on,
The transistor Q ₄ whose base B is common to Q ₁ is turned off, and the collector potential of Q ₄ rises by this off, D ₂ turns on,
D ₁ is turned off. Then, the off-time voltage holding circuit 7 operates, the gate voltage is held at (V _CC2 −V _EE ), the gate-source voltage V _GS of the junction FET JFi becomes “H”, and the junction FET JFi is turned off. It turns off.

In the analog switch circuit shown in FIGS. 2 to 4, a P-channel junction type FET JFi is used as a switching element.
The pinch-off voltage Vp of this FET is
It varies greatly from 0.7V to 2.3V. Therefore, this joining type F
To ensure that the ETJFi is turned off, the second power supply Vcc ₂ is set to the following value in consideration of the maximum value of the above-mentioned variation. That is, Vcc ₂ > Vopmax (maximum amplitude of input signal)
+ V _BE (base of the transistor Q ₃ - emitter voltage) +
2.3 [V]

FIG. 5 (A) shows the change over time of the noise output from the output terminal 3 when a signal that switches between on and off at time zero is input to the terminal Ci in FIG.
The vertical axis represents the noise peak-to-peak voltage Vpp, the horizontal axis represents time, and the second power supply voltage Vcc ₂ is used as a parameter. From this figure, it can be seen that the second power supply Vcc ₂ is
In both cases, noise starts to appear 28 μsec after signal switching, but the peak and duration of the noise are:
It can be seen that the latter is larger than the former. On the other hand, FIG.
2 (B) shows, at time zero, a signal which switches from OFF to ON to the terminal C ₁ of, for example, the junction FET JF ₁ of FIG. 2 and a signal which switches from ON to OFF to the terminal C ₂ of the junction FET JF ₂ to one ground side. When these FETs are turned on or off, the vertical axis shows the gate-source voltage V _GS applied to the FETs, and the horizontal axis shows the parameters and the parameters in FIG.
It is shown in the same manner as.

[0028] In FIG. 5 (B), the the three downhill linear (G1 waveform) shows a time when switched on FETJF ₁ from OFF, three right upstream linear (G2 waveform) is FETJF ₂ indicates a time point of switching from oN to oFF, but the vertical axis FE
In the region of 1.2 V or more corresponding to the pinch-off voltage Vp of T, the FET JFi is completely off regardless of the switching of the input signal of the terminal Ci, and similarly, in the region where the gate-source voltage V _GS is negative, the FET JFi is similarly turned off. It is completely on. Therefore,
In the region where the gate-source voltage V _GS is 0 to 1.2 V,
The second power supply voltage Vcc ₂ increases, while the delayed time of FETJF ₁ is turned on, it is seen that earlier time FETJF ₂ of one ground side is turned off. That is, in the above-mentioned region, when the second power supply voltage Vcc ₂ is 10 V or 12 V,
FETJF ₂ is but two if there is a time from off to FETJF ₁ is turned on is a long time off at the same time,
When the second power supply voltage Vcc ₂ is 8 V, the time during which both are simultaneously turned off is short. Each junction type FET which is a switching element of the analog switching circuit 1 (see FIG. 2)
If the time during which the two FETs are simultaneously turned off becomes longer due to a difference in the on / off switching timing between the JFis, noise accompanying the switching is generated as shown by Vcc ₂ = 10,12V in FIG. If the two FETs JF ₁ and JF ₂ are switched on and off in the opposite manner as described above, both FETs are simultaneously turned on for a long time for the same reason, and noise is generated.

The first condition for eliminating such noise is G
T _ON the intersection of the horizontal axis of the waveform, when the intersection of the V _GS = Vp line G2 waveform and T _OFF, is to choose a second power supply voltage Vcc ₂ such that T _ON <T _OFF, In this embodiment, Vc
the c ₂ is to 8V below. In addition, the second to eliminate noise
Is to optimize the ratio I _H / I _L of the current values flowing through the transistors Q ₂ and Q ₄ in FIG. FIG. 4 shows an example in which the ratio of the current values is optimized, and this ratio I _H /
If both current values are increased while maintaining _IL = 6, the switching speed can be increased without increasing noise at the time of switching.

FIG. 6 shows an example of a photoreceiver / amplifier incorporating the analog switch circuit 1 described with reference to FIGS. This photoreceiver / amplifier is a set of photodiodes PDi of a device having the same overall structure as described in the conventional example of FIG.
And an amplifier APi only. An analog switch circuit 1 is connected to an output terminal 2 of the amplifier APi having a feedback resistance _Rf.
, And a buffer amplifier 10 having a gain of 1 is connected to the output terminal 3 of the circuit 1. As described above, the analog switch circuit 1 is connected to the output terminal 2 of the amplifier APi and the ground V.
Two sources R ₁ and R ₂ connected in series between _EE and _EE , a source S was connected to a connection point of these resistors and the output terminal 2, and a drain D was connected to a common output terminal 3. a damping circuit consisting of two junction type FETJF _1, JF ₂ Prefecture, and a control circuit 5 for outputting a control signal for turning on and off each junction FETJF _1, JF _2. The buffer amplifier 10 can be replaced with an emitter follower circuit or a push-pull output circuit.

The above-described light receiving and amplifying device operates as follows. That is, a digital disc player (not shown)
When reading data by irradiating a laser of constant power to the lower layer of the two-layer type optical disk, the control circuit 5 causes the turn on only the junction type FETJF ₁ by a command signal from the input terminal 5a. The low current signal output from the photodiode PDi according to the low reflected light amount is converted into a voltage signal by the amplifier APi, amplified at a constant rate to a low voltage signal, and then turned on to the junction type F.
Buffer amplifier 10 without attenuation through ETJF ₁
, And is amplified with the same intensity, that is, the amplification factor 1, and is output from the output terminal 11 as a voltage signal. On the other hand, when reading the data by irradiating the upper layer of the disk, the control circuit 5 turns on only the junction FETJF _2, a high voltage signal output through the amplifier APi from photodiode PDi is a junction type FETJF ₂ ON After being attenuated, it enters the buffer amplifier 10 and is output as a voltage signal from the output terminal 11 with the same intensity. Therefore, the light receiving current of the photodiode PDi changes to a strong or weak level depending on whether the reflected light is from the upper layer or the lower layer. However, the level of the voltage signal output from the output terminal 11 does not differ between the upper and lower layers, and The obtained signals have equivalent frequency characteristics and S / N ratio characteristics.

As described above, the analog switch circuit 1 of the above-mentioned light receiving and amplifying device uses a C-MO as a switching element.
Instead of S-transistors, use junction type FETs JF ₁ and JF ₂ which have the same high input impedance as this and can be integrated on one semiconductor substrate by the same manufacturing process as other bipolar transistors as circuit elements. ing. Then, in consideration of the variation of the pinch-off voltage Vp of the junction type FET, the second operation is performed to perform an accurate on / off operation.
The power supply voltage Vcc ₂ is appropriately set, the second power supply voltage Vcc ₂ is appropriately selected in order to suppress noise in the output signal, and the second power supply voltage Vc 2 is set when the junction FET is turned off and on.
Various circuit constants are determined so that the ratio I _H / I _{L of the} current flowing from c ₂ to the ground V _EE becomes optimal (see FIG. 4). Therefore, an accurate amount of attenuation of the output signal can be obtained, and the current can flow in both directions. Therefore, the versatility is enhanced, and the analog switch circuit can be manufactured quickly and inexpensively by reducing the number of manufacturing steps.

FIG. 7 shows another example of the light receiving and amplifying device incorporating the analog switch circuit 1 described in FIGS. This light receiving and amplifying device has an overall structure similar to that described in the conventional example of FIG. 10, except that two feedback resistors _Rf are connected in parallel between the output terminal and the inverting input terminal of each amplifier APi (i = 1 to 6). , One R _f is directly connected to the other R _f , and another R _f is connected to the attenuating circuit via the analog switch circuit 12 described above.
A control terminal V as a control circuit that outputs an off control signal
m is added. FIG. 8 is a detailed circuit diagram showing a set of the photodiode PDi, the amplifier APi, the feedback resistor R _f , the analog switch circuit 12 and the control terminal Vm in FIG. 7, and the amplifier APi is configured to receive light from the photodiode PDi. A current-voltage conversion differential amplifier circuit 15 for converting a current signal into a voltage signal; a phase compensation element switching circuit 16 for performing a selected phase compensation on the signal; and an output signal from this circuit is amplified by a push-pull method. The control signal from the control terminal Vm is input to a circuit portion of the amplifier APi that outputs an on / off control signal to the gate of the junction FET 12.

The above-described light receiving and amplifying device operates as follows. That is, a digital disc player (not shown)
When data is read by irradiating the lower layer of the two-layer type optical disk with a laser having a constant power, an "H" signal is input to the control terminal Vm, that is, the power supply voltage Vcc is applied. Then, an ON control signal is output from each amplifier APi (see FIG. 8) to the junction type FET 12, and this FET 12 is turned ON, and two feedback resistors _Rf are connected in parallel to the amplifier APi.
The low current signal input from the photodiode PDi according to the low reflected light amount is amplified twice as much as when a single feedback resistor _Rf is added, and output as a voltage signal from the output terminal Vi. On the other hand, when data is read by irradiating the upper layer of the disk with the laser, a signal of "L" is input to the control terminal Vm, that is, the control terminal Vm is grounded _VEE . Then, an off control signal is output from each amplifier APi to its junction type FET 12, and this FET 12 is turned off, and only a single feedback resistor _Rf is connected to the amplifier APi. The resulting high current signal is amplified by a single factor with a single feedback resistor _Rf and output as a voltage signal from an output terminal Vi. Therefore, the light receiving current of the photodiode PDi is
The reflected light changes strongly or weakly depending on whether it is from the upper layer or the lower layer,
The level of the voltage signal output from the output terminal 11 is
The signal read without being different in the lower layer has the same frequency characteristics and S / N ratio characteristics.

The analog switch circuit 12 of the above-described light receiving and amplifying device also has the same junction type FE as a switching element in place of a C-MOS transistor as in FIG.
Because T is used, accurate output signals can be obtained with appropriate attenuation according to the upper and lower layers of data reading from the disk, and current can flow in both directions. , The analog switch circuit can be manufactured quickly and inexpensively.

In the embodiment of FIG. 2, the attenuating circuit of the first photoreceiver / amplifier of the present invention is composed of four resistors and a junction type FET. If the division ratio of each resistor is appropriately determined, an arbitrary attenuation amount can be set. Further, in the second light receiving and amplifying device of the present invention, in the embodiment of FIG. 7, each amplifier is constituted by six output channels having two parallel feedback resistors, but the number of output channels is not limited to six. Further, the number of the parallel feedback resistors having the switching element of each amplifier may be three or more so as to correspond to the recording method of three or more layers of the disk.

[0037]

As is apparent from the above description, claim 1
Analog switch circuit converts the input signal to a plurality of junction type F
Since there are provided an attenuating circuit that attenuates the output according to the on / off of the ET and outputs an output signal, and a control circuit that outputs a control signal for selecting and turning on and off the above-mentioned junction type FET, C is used as a switching element. -Instead of MOS transistors, it has a high input impedance equivalent to this, and can be integrated on a single semiconductor substrate in almost the same manufacturing process as other bipolar transistors that are elements of an analog switch circuit, so that accurate attenuation is achieved. Since a large amount of output signals can be obtained and current can flow in both directions, it is versatile and can be manufactured quickly and inexpensively by reducing the number of manufacturing steps.

According to a second aspect of the present invention, there is provided a light receiving and amplifying device having a photodiode and an amplifier for converting a light receiving current from the photodiode into a voltage and amplifying the voltage. A plurality of resistors connected in series with each other between the output of the amplifier and the ground, each source was connected to a connection point between the resistors and the output of the amplifier, and the drain was connected to a common output terminal. Since it is composed of a plurality of junction FETs, C
-An analog switch circuit using a junction type FET instead of a MOS transistor can be integrated on a single semiconductor substrate together with a bipolar transistor, and can be manufactured quickly and inexpensively, and can be universally applied to gain switching of a light receiving amplifier. Operates with high accuracy over a wide frequency band.

According to a third aspect of the present invention, there is provided a photoreceiver / amplifier having a photodiode, and an amplifier for converting a photocurrent received from the photodiode into a voltage and amplifying the voltage. The analog switch circuit according to the first aspect is provided. A resistor is connected between the output and the input of the amplifier, and a resistor and the junction FET are connected in series between the output and the input of the amplifier. The analog switch circuit using IGBTs can be integrated on a single semiconductor substrate together with bipolar transistors, can be manufactured quickly and inexpensively, and can be universally applied to gain switching of a photoreceiver / amplifier, and operates with high accuracy in a wide frequency band. I do.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of an example of an analog switch circuit according to the present invention.

FIG. 2 is a circuit diagram showing a specific example of FIG.

FIG. 3 is an equivalent circuit diagram showing details of a control circuit including one junction type FET and a terminal related thereto in the analog switch circuit of FIG. 2;

FIG. 4 is a circuit diagram showing a specific configuration and circuit constants of FIG.

FIG. 5 is a diagram showing a time lapse of noise and a turn-on / off timing generated when two junction-type FETs are switched on and off.

FIG. 6 is a circuit diagram showing an example of a light receiving and amplifying device incorporating the analog switch circuit.

FIG. 7 is a circuit diagram showing another example of the light receiving and amplifying device incorporating the analog switch circuit.

FIG. 8 is a detailed circuit diagram illustrating a set of a photodiode, an amplifier, a feedback resistor, an analog switch circuit, and a control terminal in FIG. 7;

FIG. 9 is a diagram showing an analog switch circuit used for a conventional electronic volume control.

FIG. 10 is a circuit diagram of an optical amplifying device used for a pickup of a conventional digital disk player.

FIG. 11 is a detailed circuit diagram showing a set of a photodiode and an amplifier in FIG. 10;

FIG. 12 is a flowchart illustrating a method of forming a bipolar transistor and a C-MOS transistor on one semiconductor substrate.

[Explanation of symbols]

1 ... analog switch circuit, 2 ... input terminal, 3 ... output terminal, 4 ... damping circuit, 5 ... control terminal (circuit), 10 ... buffer amplifier, 11 ... output terminal, 12 ... analog switch circuits, JF ₁ ～JF ₄ ... junction FET, R ₁ ~R ₄ ... resistors, C ₁ ~
C ₄ ... terminal, AP ₁ ~AP ₆ ... amplifier, PD ₁ ~PD ₆ ... photodiode, V ₁ ~V ₆ ... control terminal.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H04B 10/04 10/06

Claims (3)

[Claims] 1. An attenuating circuit for attenuating an input signal in accordance with on / off of a plurality of junction type FETs (field effect transistors) and outputting an output signal, and control for selecting and turning on / off the junction type FET An analog switch circuit, comprising: a control circuit that outputs a signal. 2. A light receiving and amplifying device comprising: a photodiode; and an amplifier for converting a light receiving current from the photodiode into a voltage and amplifying the voltage, comprising: an analog switch circuit according to claim 1; A plurality of resistors connected in series with each other between the ground, and a plurality of the junction types in which each source is connected to a connection point between the resistors and an output of the amplifier, and a drain is connected to a common output terminal. A light receiving and amplifying device comprising an FET. 3. A light receiving and amplifying device having a photodiode and an amplifier for converting a light receiving current from the photodiode into a voltage and amplifying the voltage, comprising: an analog switch circuit according to claim 1; A light receiving and amplifying device comprising a resistor connected between an input and a resistor and the junction FET connected in series between an output and an input of the amplifier.