CN100334811C - First-class design method for radiofrequency signal matched attenuation network - Google Patents

Abstract

The invention discloses a first-level design method of a radio frequency signal matching attenuation network. The method includes: A. measuring the load impedance of a radio frequency electronic circuit; The end of the T-type matching attenuation network is connected in parallel with the load; when the measured load impedance characteristic is capacitive, a T-type matching attenuation network composed of resistance and inductance is set, and the inductance is located at the end of the T-type matching attenuation network and connected in series with the load; C. Calculate the value of the corresponding device in the Π-type or T-type matching attenuation network according to the measured load impedance, the center frequency of the Π-type or T-type matching attenuation network and the required attenuation, and then select the corresponding device according to the value to realize Π Type or T-type matching attenuation network. The method can simply set an impedance-matched attenuation network for the radio frequency signal, thereby saving costs.

Description

A One-Level Design Method of Matched Attenuation Network for RF Signal

technical field

The invention relates to a radio frequency signal matching attenuation technology, in particular to a first-level design method of a radio frequency signal matching attenuation network.

Background technique

The wide application of wireless technology has led to the rapid development of high-frequency communication electronic circuits. In high-frequency communication electronic circuits, in order to obtain the best operating point of nonlinear devices such as frequency mixing devices, it is often necessary to control the magnitude of the radio frequency signal, and to amplify and attenuate the radio frequency signal to a certain extent. However, the continuity of RF signal transmission requires no reflections, that is, the impedance matching between the attenuation network and the transmission line must be maintained, otherwise the signal transmission will be distorted. Therefore, it is very important to set up an impedance-matched attenuation network for the RF signal.

Usually, setting the attenuation network for impedance matching for radio frequency signals is divided into two steps. The first step is to set the attenuation network for radio frequency signals, that is, to connect resistors with fixed resistance in series on the radio frequency signal electronic circuit to realize the attenuation of radio frequency signals; The first step is to set an impedance matching network for the radio frequency signal, so that there is no reflection of the radio frequency signal with the attenuation network during transmission, and keep the attenuation network of the radio frequency signal and the impedance matching of the transmission line.

However, using this method to set an impedance-matched attenuation network for the radio frequency signal has disadvantages: first, this method uses two networks to realize the attenuation and impedance matching of the radio frequency signal respectively, and adds an attenuation network for setting impedance matching for the radio frequency signal Second, this method uses two networks to realize the attenuation and impedance matching of the radio frequency signal, which increases the layout area of the printed board for arranging the radio frequency signal, and wastes the cost.

Contents of the invention

In view of this, the main purpose of the present invention is to provide a first-level design method of a radio frequency signal matching attenuation network, which can easily set an impedance matching attenuation network for radio frequency signals, thereby saving costs.

According to above-mentioned purpose, specific embodiment of the present invention is as follows:

A method for realizing a radio frequency signal primary matching attenuation network, the method comprising:

A. Pre-measure the load impedance of the radio frequency electronic circuit;

B. When the measured load impedance characteristic is inductive, set a ∏-type matching attenuation network composed of three resistors and capacitors, where three resistors form the ∏-type of the ∏-type matching attenuation network, and the capacitor is located in the ∏-type The end of the matching attenuation network is connected in parallel with the load; when the measured load impedance characteristic is capacitive, a T-type matching attenuation network composed of three resistors and inductance connections is set up, and the three resistors form the T-type matching attenuation network. T-type, the inductor is located at the end of the T-type matching attenuation network and connected in series with the load;

C. Use the load impedance measured in step A, the center frequency of the Π-type or T-type matching attenuation network and the set attenuation to calculate the value of the corresponding device in the Π-type or T-type matching attenuation network, and then select the corresponding The device implements a Π-type or T-type matching attenuation network.

The process of calculating the value of the corresponding device in the Π-type matching attenuation network is:

Calculate the admittance value of the load according to the reactance value in the load impedance measured in step A or measure the admittance value Y _L -jG _L of the load with a network analyzer, and the shunt capacitor offsets the inductive reactance of the load. The admittance value of the capacitive device in the Π-type matching attenuation network G22= _GL , if the center frequency of the Π-type matching attenuating network is set to f ₀ , then the capacitance C of the capacitive device is C=G22/2πf ₀ ;

Set the transmission coefficient of the ∏-type matching attenuation network as the attenuation, and the reflection coefficient of the ∏-type matching attenuation network is 0, and substitute the set attenuation and reflection coefficient into the ∏-type matching attenuation network to calculate the The admittance value of the resistive device in the circuit.

The process of calculating the value of the corresponding device in the T-type matching attenuation network is:

The reactance value in the load impedance measured in step A is capacitive, and the load is Z _L -jX _L . The series inductance cancels the capacitive reactance of the load, which is the reactance value X22=X _L of the inductance device in the T-type matching attenuation network. Set the The center frequency of the T-type matching attenuation network is f ₀ , then the inductance value W of the inductance device is W=X22/2πf ₀ ;

Set the transmission coefficient of the T-type matching attenuation network as the attenuation, and the reflection coefficient of the T-type matching attenuation network is 0. Substitute the set attenuation and reflection coefficient into the T-type matching attenuation network, and then calculate the T-type matching attenuation network. The reactance value of the resistive device in the branch.

The capacitor described in step B is replaced with a low-resistance microstrip line.

The inductance described in step B is replaced by a high-resistance microstrip line.

Measure the load impedance of the RF signal electronic circuit described in step A with a network analyzer.

The method further includes: using a network analyzer to debug the set Π-type or T-type matching attenuation network, so that the Π-type or T-type matching attenuation network meets the requirements of the radio frequency electronic circuit system.

The present invention adopts a first-level network to set a matching attenuation network for the radio frequency signal, and sets different matching attenuation networks according to the reactance characteristics presented by the load on the radio frequency signal electronic circuit: when the reactance characteristic of the load is inductive, set a capacitive ∏ type matching attenuation network ; When the reactance characteristic of the load is capacitive, set the inductive T-type matching attenuation network. According to the radio frequency signal electronic circuit and the required attenuation, calculate the device value of the corresponding device in the ∏-type matching attenuation network or the T-type matching attenuation network, and set the ∏-type matching attenuation network or the T-type matching attenuation network according to the device value of the corresponding device corresponding devices in . The method provided by the invention conveniently sets a matching attenuation network for radio frequency signals, reduces the use of printed boards, and saves costs.

Description of drawings

Figure 1 is a schematic diagram of a Π-type matching attenuation network.

FIG. 2 is a schematic diagram of an attenuation network using T-shaped matching.

Figure 3 is a structural diagram of a microstrip line.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail by citing the following embodiments and referring to the accompanying drawings.

The method provided by the invention first selects the attenuation network type according to the actual load characteristics of the radio frequency electronic circuit, and determines whether to use the T-type attenuation network or the Π-type attenuation network. The invention first offsets the imaginary reactance part of the load, that is, when the measured load impedance characteristic is inductive, parallel capacitors are connected; the load impedance is capacitive series inductance, so that only the real part of the load exists, and then the matching attenuation is realized through the resistance network. Specifically, when the load impedance characteristic is inductive, set a ∏-type matching attenuation network composed of a resistor and a capacitor, and the capacitor is located at the end of the ∏-type matching attenuation network in parallel with the load; when the measured load impedance characteristic is capacitive, A T-shaped matching attenuation network composed of a resistor and an inductance is set, and the inductance is located at the end of the T-shaped matching attenuation network and connected in series with the load. Then calculate the parameter value of each component of the attenuation network according to the actual load and the required RF signal power attenuation, and finally select the corresponding package of the component according to the power tolerance of the RF signal transmission of the RF electronic circuit and the calculated parameter value of each component Implement an attenuating matching network.

The procedure for setting up a matched attenuation network for an RF signal is as follows:

Step 1. Determine the center frequency of the matching attenuation network, and set the center frequency to f ₀ , for example: when the radio frequency signal is used in the field of wireless LAN communication, use a center frequency of 2.45GHz. Step 2. Use a network analyzer to measure the radio frequency signal electronics The impedance of the actual load of the circuit at the center frequency is ZL=RL+jXL, where XL is the reactance value;

Step 3. Select the form of the attenuation network according to the measured load impedance. When the XL of the impedance is positive, the load impedance is inductive. Use a Π-type matching attenuation network and go to step 4; when the XL of the impedance is negative value, the load impedance is capacitive, use a T-type matching attenuation network, and go to step 8;

Step 4. As shown in Figure 1, Figure 1 is a schematic diagram of a Π-type matching attenuation network: the matching attenuation network is composed of three resistance devices R1, R2, R3 and a capacitor device C1, and the network is directly connected in parallel with the load. The matching attenuation network is shaped like a ∏ type, and the admittance value of the resistance device R1 is Y11, the admittance value of the resistance device R2 is Y12, the admittance value of the resistance device R3 is Y22, and the admittance value of the capacitance device C1 is G22. ;

Step 5. Use a network analyzer to measure or calculate the admittance of the load as Y _L -jG _L according to the impedance of the load, and determine the admittance value of the capacitive device C1 of the matching attenuation network to be G22, namely

G22＝GL (1)

That is, the admittance value G22 of the matching attenuation network is equal to the negative number of the load admittance value of the measured radio frequency electronic circuit, and the sum of the two is 0 for the imaginary part, which offsets the reactance factor of the load;

Step 6. Set the value of the attenuation S21 of the RF signal matching attenuation network, and calculate the admittance value of each device in the Π-type matching attenuation network, that is, calculate Y11, Y12 and Y22. The calculation process is as follows:

The RF signal matching attenuation network must match the RF signal electronic circuit, so the reflection coefficient S11 of the RF signal matching attenuation network is 0, ensuring that the resistance value after adding the matching attenuation network to the RF signal electronic circuit is 50 ohms, that is, the matching attenuation network The port admittance value YN11=1/50, its YN11 is:

YN11=(Y22+YL)*Y12/(Y12+Y22+YL)+Y11=1/50, (2);

According to the reciprocity principle of the passive network, the transmission coefficient S12 of the RF signal matching attenuation network is equal to the network attenuation S21, then:

Y11=Y22+YL, (3);

S21＝Y12*Y11/(2*Y11*Y12+Y11*Y11),   (4);

Calculate Y11, Y12 and Y22 according to formulas (2), (3) and (4);

Step 7. According to the calculated values of Y11, Y12, and Y22, the resistance of the matching attenuation network is respectively set by using a resistance device, and the capacitance of the matching attenuation network is set by using a concentrated element capacitor or a microstrip line according to the value of G22;

Step 8, as shown in Figure 2, Figure 2 is a schematic diagram of an attenuation network using T-type matching, the matching attenuation network is composed of three resistance devices R11, R21, R31 and an inductance device W1, the network is directly connected to the load Inductance is connected in the branch. Respectively set the impedance value of the resistance device R11 to Z11, the resistance value of the resistance device R21 to Z12, the resistance value of the resistance device R31 to Z22 and the reactance value of the inductance device W1 to X22;

Step 9, determine the reactance value of the inductance device W1 of the matching attenuation network X22, namely

X22＝XL (5)

That is, the reactance value X22 of the inductance device W1 of the matching attenuation network is equal to the negative number of the load reactance value of the measured radio frequency electronic circuit, and the sum of the two is 0 for the imaginary part to offset the reactance of the load;

Step 10, set the value of the attenuation S21 of the RF signal matching attenuation network, and calculate the impedance value of each device in the attenuation network of the T-type match, that is, calculate Z11, Z12 and Z22, and the calculation process is as follows:

The RF signal matching attenuation network must match the post-stage output circuit of the RF signal, so the reflection coefficient S11 of the RF signal matching attenuation network is 0, that is, the impedance value of the matching attenuation network port ZN11=50, and its ZN11 is:

ZN11=Z11+Z12*(Z22+RL)/(Z12+Z22+RL)=50, (6);

The transmission coefficient S21 of the RF signal matching attenuation network is equal to the network attenuation S21. According to the reciprocity principle of the passive network, then:

Z11=Z22+RL, (7);

S21＝Z12*Z11/(2*Z11*Z12+Z11*Z11), (8);

Calculate Z11, Z12 and Z22 according to formulas (5), (6), (7) and (8);

Step 11, select resistance elements according to the calculated Z11, Z12 and Z22 to realize the resistance of the matching attenuation network, and use a concentrated element inductance or a microstrip line to realize the series inductance of the matching attenuation network according to the calculated X22, and use a network analyzer to analyze The set matching attenuation network is debugged and tested, and the matching attenuation network in practical application is obtained.

In the Π-type matching attenuation network, a capacitor is used to realize the reactance part in the matching attenuation network, and the capacitance value of capacitor C1 is calculated as follows:

C=G22/2πf ₀ (9);

In the T-type matching attenuation network, the inductance is used to realize the reactance part in the matching attenuation network, and the inductance W1 value of the inductor is calculated as follows:

W=X22/2πf ₀ (10).

The present invention can also use the microstrip line to realize the parallel connection of capacitors in the Π-type matching attenuation network and the series connection of inductance in the T-type matching attenuation network. The structure of the microstrip line is shown in Figure 3: the microstrip line is composed of a signal transmission line with a width of w, a signal insulation medium with a height of h, and a signal transmission ground line.

In the Π-type matching attenuation network, a short low-impedance transmission line is used to realize parallel capacitance, that is, a section of low-impedance transmission line is placed at the place where the parallel capacitor is connected, the impedance value of the low-impedance transmission line is set to Z, and the width of the low-impedance transmission line is set to w , set the insulation height of the low-resistance transmission line as h, and its w is less than h, then the height and width of the transmission line are calculated as follows:

Z＝60ln(8h/w+w/4h)          (11),

Z=120π/(w/h+2.42-0.44h/w+(1-h/w) ⁶ (12),

The line height and line width of the low-resistance transmission line can be calculated according to formulas (11) and (12).

The line length of this low resistance transmission line is calculated as follows:

ε _e = (1+ε _r )/2+(ε _r -1)/2/(1+10h/w) ^0.5 (13),

λg=C light speed/(ε _e *f0) (14),

The length of the transmission line is: l＝G22*Z*λg/(2π) (15);

In the T-type matching attenuation network, a short high-impedance transmission line is used to realize the series inductance, that is, a section of high-impedance transmission line is placed at the place where the inductor is placed, and the impedance value of the high-impedance transmission line is set to Z, and the width of the high-impedance transmission line is set to w , set the insulating medium height of the resistance transmission line as h, and its w is less than h, then the height and width of the transmission line can be calculated according to formula (13) and formula (14)

The length of the high resistance transmission line is: l=X22*λg/(2πZ) (16);

Substitute formula (13) and formula (14) into formula (16) to calculate the line length of the high-impedance transmission line.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention. within the scope of protection.

Claims (7)

1, a kind of one-level design method of radio frequency signal matching attenuation network, it is characterized in that, this method comprises: A. Pre-measure the load impedance of the radio frequency signal electronic circuit; B. When the measured load impedance characteristic is inductive, set a ∏-type matching attenuation network composed of three resistors and capacitors, where three resistors form the ∏-type of the ∏-type matching attenuation network, and the capacitor is located in the ∏-type The end of the matching attenuation network is connected in parallel with the load; when the measured load impedance characteristic is capacitive, a T-type matching attenuation network composed of three resistors and inductance connections is set up, and the three resistors form the T of the T-type matching attenuation network. type, the inductor is located at the end of the T-type matching attenuation network and connected in series with the load; C. Use the load impedance measured in step A, the center frequency of the Π-type or T-type matching attenuation network and the set attenuation to calculate the value of the corresponding device in the Π-type or T-type matching attenuation network, and then select the corresponding The device implements a Π-type or T-type matching attenuation network. 2. The method according to claim 1, wherein the process of calculating the value of the corresponding device in the ∏ type matching attenuation network is: According to the reactance value in the load impedance measured in step A, calculate the admittance value of the load or measure the admittance value Y _L -jG _L of the load with a network analyzer, and connect the parallel capacitor to offset the inductance of the load Impedance is the admittance value G22 of the capacitive device in the ∏-type matching attenuation network G22=G _L , setting the center frequency of the ∏-type matching attenuating network as f ₀ , then the capacitance C of the capacitive device is C=G22/2πf ₀ ; Set the transmission coefficient of the ∏-type matching attenuation network as the attenuation, and the reflection coefficient of the ∏-type matching attenuation network is 0, and substitute the set attenuation and reflection coefficient into the ∏-type matching attenuation network to calculate the The admittance value of the resistive device in the circuit. 3. The method according to claim 1, wherein the process of calculating the value of the corresponding device in the T-type matching attenuation network is: The reactance value in the load impedance measured in step A is capacitive, and the load is Z _L -jX _L . The series inductance cancels the capacitive reactance of the load, which is the reactance value X22=X _L of the inductance device in the T-type matching attenuation network. Set the The center frequency of the T-type matching attenuation network is f ₀ , then the inductance value W of the inductance device is W=X22/2πf ₀ ; Set the transmission coefficient of the T-type matching attenuation network as the attenuation, and the reflection coefficient of the T-type matching attenuation network is 0. Substitute the set attenuation and reflection coefficient into the T-type matching attenuation network, and then calculate the T-type matching attenuation network. The reactance value of the resistive device in the branch. 4. The method according to claim 1, characterized in that the capacitor in step B is replaced by a low-resistance microstrip line. 5. The method according to claim 1, wherein the inductance in step B is replaced by a high-resistance microstrip line. 6. The method according to claim 1, characterized in that a network analyzer is used to measure the load impedance of the radio frequency signal electronic circuit in step A. 7. The method according to claim 1, further comprising: using a network analyzer to debug the set Π-type or T-type matching attenuation network, so that the Π-type or T-type matching attenuation network meets the requirements of communication electronic circuits System usage.

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