JPH05315961A - A/d conversion circuit - Google Patents

Abstract

PURPOSE:To shorten circuitry by eliminating an automatic again adjusting circuit and to provide an A/D conversion circuit improved in its SN ratio. CONSTITUTION:Analog voltage Vi is amplified by an amplifier circuit 1 and the amplified voltage is inputted to an analog voltage input terminal 51 of an A/D converter 8 and simultaneously inputted also to the input terminal of a detector 7. The analog voltage outputted from the circuit 1 is detected and the detected output voltage is supplied as a bias voltage for the circuit 1 and supplied also to the a reference voltage input terminal 52 of the A/D converter 8. The amplified output voltage from the circuit 1 is inputted to the terminal 51 by using the detected output voltage inputted to the terminal 52 as a full range. Since the level of the detected output voltage follows the level variation of the voltage level of the analog voltage Vi, the analog output voltage of the circuit 1 can be inputted to the A/D converter in the scale of an always appropriate level without being influenced by the level variation of the analog voltage Vi.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D conversion circuit.

[0002]

2. Description of the Related Art A conventional A / D conversion circuit has an analog input voltage V as shown in the block diagram of FIG.
Corresponding to _i , an automatic gain adjustment circuit 9 including a variable gain amplifier 10, an amplification circuit 11, a detector 17, and a reference voltage source 18, and an A / D converter 19 are provided. The amplifier circuit 11 is composed of a capacitor 12, an amplifier 13, and resistors 14 to 16.

The analog input voltage V _i is input to and amplified by the variable gain amplifier 10, and its output voltage is amplified by the amplifier circuit 1.
Input to 1. In the amplifier circuit 11, the analog voltage output from the variable gain amplifier 10 is amplified by the amplifier 13 with the reference voltage V _r applied from the reference voltage source 18 as a positive bias voltage, and the analog voltage output from the A / D converter 19 is amplified. It is input to the analog voltage input terminal 53, and at the same time, the detector 1
7 is input to the input terminal. In the detector 17, the analog voltage amplified by the amplifier circuit 11 is detected, the detected output voltage is fed back to the variable gain amplifier 10, and the gain of the variable gain amplifier 10 is controlled and adjusted. The analog voltage input to the input terminal of the / D converter 19 is maintained at a constant level. Also, A / D
The reference voltage input terminal 54 of the converter 19 is connected to the reference voltage source 1
The reference voltage V _{r of} 8 is supplied.

Thus, in the A / D converter 19,
Analog voltage input terminal 53 and reference voltage input terminal 54
Receiving the above input voltage for the analog input voltage V
_The desired digital output signal Vo corresponding to _i is output.

In this conventional example, the A / D converter 19
The level of the analog voltage input to the input terminal 53 of
As described above, even when the level of the input analog voltage V _i fluctuates through the output voltage control action of the automatic gain adjustment circuit 9, the output voltage is A / D as an analog voltage of a constant voltage level. It is input to the converter 18.

[0006]

DISCLOSURE OF THE INVENTION The above-mentioned conventional A / D
In the conversion circuit, as shown in FIG. 2, an automatic gain adjustment circuit 9 including a variable gain amplifier 10, an amplification circuit 11, a detector 17 and a reference voltage source 18 is an A / A circuit.
Since it is provided as an input circuit to the D converter 19, there is a drawback that the noise voltage level input accompanying the analog input voltage V _i becomes large and the S / N ratio at the output side is lowered. Further, the existence of the automatic gain adjustment circuit has a drawback that the circuit scale of the A / D conversion circuit becomes large and complicated.

[0007]

An A / D conversion circuit of the present invention amplifies and outputs an analog input voltage to be A / D converted, and outputs the analog amplified output voltage to a predetermined A / D.
An amplifier circuit that supplies the analog voltage input terminal of the converter,
An analog amplified output voltage output from the amplifier circuit is detected and output, and the detected output voltage is supplied to the reference voltage input terminal of the A / D converter and supplied to the amplifier circuit as a bias voltage. And a circuit as an input circuit to at least the A / D converter.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. As shown in FIG. 1, in this embodiment, an amplifier circuit 1 including a capacitor 2, an amplifier 3, and resistors 4 to 6,
The detector 7 and the A / D converter 8 are provided.

In FIG. 1, the input analog voltage V
_{The i} is input to and amplified by the amplifier circuit 1, and its output voltage is input to the analog voltage input terminal 51 of the A / D converter 8 and simultaneously to the input terminal of the detector 7. In the detector 7, the analog voltage output from the amplifier circuit 1 is detected, and the detected output voltage is supplied as the bias voltage of the amplifier circuit 1 and is supplied to the reference voltage input terminal 52 of the A / D converter 8. Supplied. In such a voltage input state, in the A / D converter 8, the detected output voltage input to the reference voltage input terminal 52 is set as a full range and is amplified by the amplifier circuit 1 to the analog voltage input terminal 51. The input analog output voltage is captured. In this case, even when the voltage level of the input analog voltage V _i is fluctuating, the level of the detection output voltage changes following the level fluctuation of the analog voltage V _i , so that the analog voltage V _i is changed. The analog output voltage of the amplifier circuit 1 can always be taken in on the scale of an appropriate level without being affected by the level fluctuation of V _i . As a result, A corresponding to the above input voltage
/ More D converter 8, proper A / D converted digital output V _o corresponding to the analog input voltage V _i is output.

3 (a), 3 (b) and 3 (c) respectively show the analog input voltage V _i and the reference voltage input terminal 52 of the A / D converter 8 in this embodiment, respectively. 6 is a voltage waveform diagram of a detection output voltage and an amplified output voltage input to an analog voltage input terminal 51. FIG.

[0012]

As described above, according to the present invention, the amplified output voltage of the analog input voltage and the detected output voltage of the analog input voltage are input to the input terminal and the reference voltage input terminal of the A / D converter, respectively. By doing so, there is an effect that the conventional automatic gain adjustment circuit is not required, the circuit configuration is simplified, the noise level on the output side is reduced, and the S / N ratio is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a voltage waveform diagram of each part in the one embodiment.

[Explanation of symbols]

 1, 11 Amplification circuit 2, 12 Capacitor 3, 13 Amplifier 4-6, 14-16 Resistor 7, 17 Detector 8, 19 A / D converter 9 Automatic gain adjustment circuit 10 Gain variable amplifier 18 Reference voltage source

Claims (1)

[Claims] 1. An amplifier circuit that amplifies and outputs an analog input voltage to be A / D converted, and supplies the analog amplified output voltage to an analog voltage input terminal of a predetermined A / D converter, A detection circuit that detects and outputs an analog amplification output voltage output from an amplification circuit, supplies the detection output voltage to a reference voltage input terminal of the A / D converter, and supplies the detection voltage as a bias voltage to the amplification circuit. And at least as an input circuit to the A / D converter.