CN109245728B - Double-coupling double-mixing intermediate frequency signal power feedback circuit - Google Patents
Double-coupling double-mixing intermediate frequency signal power feedback circuit Download PDFInfo
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
- H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
- H03D7/16—Multiple-frequency-changing
- H03D7/165—Multiple-frequency-changing at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature
- H03D7/166—Multiple-frequency-changing at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature using two or more quadrature frequency translation stages
- H03D7/168—Multiple-frequency-changing at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature using two or more quadrature frequency translation stages using a feedback loop containing mixers or demodulators
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Abstract
The invention discloses a double-coupling double-mixing intermediate frequency signal power feedback circuit, and belongs to the technical field of radio frequency microwave circuits. The circuit comprises a first coupler, a second coupler, a first frequency mixer, a second frequency mixer, a first amplitude control unit, a second amplitude control unit, a voltage-controlled temperature compensation crystal oscillator, a digital step attenuator and a low-pass filter. The radio frequency signal is coupled and output by the first coupler, the amplitude of the coupled and output signal is changed by the first amplitude control unit and is connected to the local oscillator port of the first frequency mixer, and the local oscillator output signal is up-converted by the crystal oscillator output signal connected to the intermediate frequency port of the first frequency mixer; the up-conversion signal output by the radio frequency port of the first frequency mixer is connected to the local oscillator port of the second frequency mixer through the second amplitude control unit, the down-conversion of the radio frequency output coupling signal connected to the radio frequency port of the second frequency mixer is carried out, and the level of the radio frequency output signal is fed back and adjusted by detecting the power amplitude of the intermediate frequency signal output from the intermediate frequency port of the second frequency mixer.
Description
Technical Field
The invention belongs to the technical field of radio frequency microwave circuits, is applied to an automatic level control system in a microwave signal generator, and particularly relates to a double-coupling double-mixing intermediate frequency signal power feedback circuit.
Background
The Automatic level Control system (Automatic L evel Control, A L C) is the key to realizing the power accuracy, power flatness, power resolution and amplitude modulation index of the signal generator.
In the entire automatic level control system, an important component constituting the power feedback loop is a detector. Detectors, which are devices that detect some useful information in a fluctuating signal, are devices that identify waves, oscillations, the presence or changes of the signal. The output signal level of the detector in the system has a certain proportional relation with the radio frequency output signal level, and the error signal of the detector and the reference level pass through the error amplifier and then control the linear modulator to correct the level of the radio frequency output signal. However, this type of power feedback loop has a major limitation: the amplitude modulation dynamic range is limited by the level detector and associated circuitry, which is typically much lower than the power variable range of a linear modulator.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a double-coupling double-mixing intermediate frequency signal power feedback circuit suitable for an automatic level control system. The circuit of the invention omits a detector which mainly limits the amplitude modulation dynamic range, can realize the adjustment of the power amplitude of the radio frequency output signal by detecting the feedback power of the fixed intermediate frequency signal, and simultaneously realizes a wider amplitude modulation dynamic range.
The technical problem proposed by the invention is solved as follows:
a double-coupling double-mixing intermediate frequency signal power feedback circuit comprises a first coupler, a second coupler, a first mixer, a second mixer, a first amplitude control unit, a second amplitude control unit, a voltage-controlled temperature compensation crystal oscillator, a digital step attenuator and a low-pass filter;
the coupling end of the first coupler is connected with the input end of the first amplitude control unit, the output end of the first amplitude control unit is connected with the local oscillator port of the first frequency mixer, the voltage-controlled temperature compensation crystal oscillator is connected with the intermediate frequency port of the first frequency mixer, the radio frequency port of the first frequency mixer is connected with the input end of the second amplitude control unit, and the output end of the second amplitude control unit is connected with the local oscillator port of the second frequency mixer;
the direct connection end of the first coupler is connected with the input end of the digital step attenuator, the output end of the digital step attenuator is connected with the input end of the second coupler, the coupling end of the second coupler is connected with the radio frequency port of the second mixer, and the intermediate frequency port of the second mixer is connected with the input port of the low-pass filter.
The radio frequency signal is input from the input port of the first coupler, and the coupling end of the first coupler outputs a radio frequency input coupling signal; the radio frequency input coupling signal is regulated and controlled by the first amplitude control unit and then input to a local oscillator port of the first frequency mixer, and a crystal oscillator signal generated by the voltage-controlled temperature compensation crystal oscillator is input to an intermediate frequency port of the first frequency mixer; the first frequency mixer up-converts signals of a local oscillator port and an intermediate frequency port of the first frequency mixer and outputs the signals from a radio frequency port; the second amplitude control unit regulates and controls the output signal of the radio frequency port of the first frequency mixer and then inputs the regulated and controlled output signal to the local oscillation port of the second frequency mixer;
the digital step attenuator performs power attenuation regulation and control on a through port signal of the first coupler; the signal after attenuation regulation is input to an input port of the second coupler, one part of radio frequency signal is directly output from a through port of the second coupler, and the other part of radio frequency signal is coupled and output from a coupling port of the second coupler to obtain a radio frequency output coupling signal; the radio frequency output coupling signal is input to a radio frequency port of a second mixer, and the second mixer performs down-conversion on signals of a local oscillator port and the radio frequency port of the second mixer and outputs the signals from the intermediate frequency port; and the low-pass filter filters the output signal of the intermediate frequency port of the second mixer to obtain a final intermediate frequency signal.
The first amplitude control unit is a first gain module.
The second amplitude control unit comprises a second gain module and a resistance type attenuation network which are cascaded.
The resistance type attenuation network is connected by three patch resistors in a pi type.
The controllable attenuation of the digital step attenuator is 31.5dB, and the step is 0.5 dB.
The low-pass filter is a patch filter, the insertion loss of the low-pass filter to 54MHz intermediate frequency signals is about 0.33dB, and the out-of-band rejection to 2-4 GHz radio frequency signals is more than 42 dBc.
The frequency of the radio frequency signal is 2 GHz-4 GHz, and the frequency of the intermediate frequency signal is 54 MHz.
The first coupler and the second coupler are of the same type.
The first mixer and the second mixer are the same in type selection.
The first power gain module and the second power gain module have the same selection type.
The invention has the beneficial effects that:
(1) the invention does not use a detector in the realization circuit, removes the limitation of the detector and realizes a wider amplitude modulation dynamic range;
(2) the invention realizes that the first coupler and the second coupler used in the circuit have the same type selection, and the first mixer and the second mixer have the same type selection, thereby ensuring good linear relation between a radio frequency output signal and an intermediate frequency signal output by a power feedback loop and having a certain stray suppression effect;
(3) the radio frequency input signal is a broadband signal, and the invention only needs to detect the power amplitude of the fixed intermediate frequency signal output by the power feedback loop to achieve the level control of the radio frequency output signal.
Drawings
FIG. 1 is a block circuit diagram of the feedback circuit of the present invention;
FIG. 2 is an ADS simulation schematic diagram of the feedback circuit of the present invention;
FIG. 3 is a diagram of ADS simulation results of the feedback circuit of the present invention;
FIG. 4 is a diagram of a real world board of the feedback circuit of the present invention;
fig. 5 is a real object test chart of the feedback circuit according to the present invention.
Detailed Description
The invention is further described below with reference to the figures and examples.
The present embodiment provides a double-coupled double-mixing intermediate frequency signal power feedback circuit, a circuit block diagram of which is shown in fig. 1, and the circuit block diagram of which includes a first coupler 10, a second coupler 11, a first mixer 20, a second mixer 21, a first amplitude control unit 30, a second amplitude control unit 40, a voltage-controlled temperature compensation crystal oscillator 50, a digital step attenuator 60, and a low-pass filter 70;
a coupling end of the first coupler 10 is connected to an input end of a first amplitude control unit 30, an output end of the first amplitude control unit 30 is connected to a local oscillator port of the first frequency mixer 20, the voltage-controlled temperature compensation crystal oscillator 50 is connected to an intermediate frequency port of the first frequency mixer 20, a radio frequency port of the first frequency mixer 20 is connected to an input end of a second amplitude control unit 40, and an output end of the second amplitude control unit 40 is connected to a local oscillator port of the second frequency mixer 21;
the direct connection end of the first coupler 10 is connected with the input end of the digital step attenuator 60, the output end of the digital step attenuator 60 is connected with the input end of the second coupler 11, and the coupling end of the second coupler 11 is connected with the radio frequency port of the second mixer 21; the intermediate frequency port of the second mixer 21 is connected to the input port of the low pass filter 70.
Inputting a 2-4 GHz radio frequency signal from an input port of the first coupler 10, and outputting a radio frequency input coupling signal from a coupling end of the first coupler 10; the radio frequency input coupling signal is regulated by the first amplitude control unit 30 and then input to the local oscillator port of the first frequency mixer 20, and a 54MHz crystal oscillator signal generated by the voltage-controlled temperature compensation crystal oscillator 50 is input to the intermediate frequency port of the first frequency mixer 20; the first mixer 20 up-converts the signals of the local oscillator port and the intermediate frequency port and outputs the signals from the radio frequency port; the second amplitude control unit 40 regulates and controls the output signal of the radio frequency port of the first frequency mixer 20 and inputs the regulated output signal to the local oscillation port of the second frequency mixer 21;
the digital step attenuator 60 performs power attenuation regulation and control on the through port signal of the first coupler 10, and the regulation and control range is 3 dB-31.5 dB, wherein the initial 3dB of the regulation and control range is the inherent insertion loss of the chip, and the final 31.5dB of the regulation and control range is the maximum attenuation which can be regulated and controlled by the chip; the signal after attenuation regulation is input to an input port of the second coupler 11, a part of radio frequency signals are directly output from a through port of the second coupler 11, and the other part of radio frequency signals are output from a coupling port of the second coupler 11, so that radio frequency output coupling signals are obtained; the radio frequency output coupling signal is input to a radio frequency port of the second mixer 21, and the second mixer 21 down-converts the signals of the local oscillator port and the radio frequency port and outputs the signals from the intermediate frequency port; the low-pass filter 70 filters the output signal of the intermediate frequency port of the second mixer 21, and filters out the image frequency with a higher frequency band and other spurious signals, so as to obtain a pure intermediate frequency signal with a frequency of 54MHz from the output port of the low-pass filter 70.
The first amplitude control unit is a first gain module.
The second amplitude control unit comprises a second gain module and a resistance type attenuation network which are cascaded.
The resistor type attenuation network is formed by connecting three chip resistors with the packaging size of 0402(1.00mm x 0.5mm) in a pi type, the resistance values of R1 and R3 of two pins of the pi type are the same and are 130 omega, and the resistance value of R2 in the middle of the top of the pi type is 44.2 omega.
The controllable attenuation of the digital step attenuator is 31.5dB, and the step is 0.5 dB.
The low-pass filter is a patch filter, the insertion loss of the low-pass filter to 54MHz intermediate frequency signals is about 0.33dB, and the out-of-band rejection to 2-4 GHz radio frequency signals is more than 42 dBc.
An ADS simulation principle diagram of the circuit is shown in FIG. 2, and comprises a harmonic balance simulation control HB1, a variable and equation control VAR1, a 2-4 GHz radio frequency signal frequency source control PORT1, a first coupler three-PORT network control SNP1, a second coupler three-PORT network control SNP2, a first gain module two-PORT network control SNP3, a second gain module two-PORT network control SNP4, a low-pass filter two-PORT network control SNP5, a first mixer control MIX1, a second mixer MIX2, a 54MHz crystal oscillator signal frequency source control PORT2 equivalent to a temperature-controlled complementary crystal oscillator, a control ATTEN1 equivalent to a digital step attenuator, resistors R1, a radio frequency signal 50 control matching output PORT Term 1 and a radio frequency signal 50 matching output PORT Term 1, a frequency control and a radio frequency signal 50 matching output PORT Term 4. radio frequency signal frequency source control, an ideal frequency gain control SNP1, a second mixer three-frequency gain control SNP PORT1, a second mixer three-PORT network control SNP # 1, a second mixer 3, a third frequency gain control and a third frequency gain control dBX 1, a third frequency filter 1, a third frequency gain module dBX-1, a third frequency source control, a third frequency filter, a third frequency gain module, a third frequency filter, a third frequency gain module, a third frequency filter, a third frequency gain module, a third frequency filter.
The ADS simulation result diagram of the power feedback circuit of the invention is shown in FIG. 3, which is composed of three sub-diagrams, respectively: a relation curve (3-1) of the radio frequency output signal power and the attenuation x of the digital step attenuator, a relation curve (3-2) of the intermediate frequency signal power and the attenuation x of the digital step attenuator, and a relation curve (3-3) of the intermediate frequency signal power and the radio frequency output signal power.
The abscissa of the sub-graph (3-1) is the attenuation x controlled by the digital step attenuator 60, the variation range is 3-30, the step is 1, and the unit is dB. The ordinate of the sub-graph (3-1) is the radio frequency output signal power which changes along with the change of the attenuation x controlled by the digital step attenuator 60, the change range is 8.10 to-18.97, and the unit is dBm. As can be seen from the sub-diagram (3-1), the rf output signal power has a good linear relationship with the attenuation x controlled by the digital step attenuator 60. The abscissa of the sub-graph (3-2) is the attenuation x controlled by the digital step attenuator 60, the variation range is 3-30, the step is 1, and the unit is dB. The ordinate of the sub-graph (3-2) is the power of the intermediate frequency signal which changes along with the change of the attenuation x controlled by the digital step attenuator 60, the change range is-16.93 to-44.06, and the unit is dBm. As can be seen from the graph (3-2), the power of the if signal has a good linear relationship with the attenuation x controlled by the digital step attenuator 60. The abscissa of the subgraph (3-3) is the radio frequency output signal power, namely the ordinate of the subgraph (3-1), the variation range is-18.97-8.10, and the unit is dBm. The ordinate of the subgraph (3-3) is the intermediate frequency signal power, namely the ordinate of the subgraph (3-2), the variation range is-44.06 to-16.93, and the unit is dBm. As can be seen from the sub-diagram (3-3), the power of the intermediate frequency signal and the power of the radio frequency output signal have a good linear relationship, so that the power amplitude of the radio frequency output signal can be feedback-adjusted by detecting the power amplitude of the 54MHz fixed intermediate frequency signal.
The physical board of the feedback circuit of the present invention is shown in FIG. 4, and the board used is FR4 board with a thickness of 20mil and a dielectric constant of 4.4. The object circuit comprises: the system comprises a first coupler 10, a second coupler 11, a first mixer 20, a second mixer 21, a first gain module 31, a second gain module 41, a resistance type attenuation network 42, a voltage-controlled temperature compensation crystal oscillator 50, a digital step attenuator 60, a low-pass filter 70, a digital control port 88, a power supply 99, a radio frequency input SMA1, a radio frequency output SMA2 and an intermediate frequency output SMA 3. The digital control port 88 is a socket for connecting the real-time circuit board and the development board, and is used for controlling the real-time attenuation x of the digital step attenuator 60, the variation range is 3-30, the step is 1, and the unit is dB. The input voltage of the power supply 99 is +6.6V, and the output voltage is + 5.0V.
The real object test chart of the feedback circuit is shown in fig. 5, the abscissa of the test chart is the radio frequency output signal power (RF _ out), the variation range is-22.33-4.67, and the unit is dBm. The ordinate of the test chart is the intermediate frequency signal power (IF _ out), and the variation range is-48.78-22.09, and the unit is dBm. From the real object test chart, the power of the intermediate frequency signal and the power of the radio frequency output signal also form a good linear relation, so that the power amplitude of the radio frequency output signal can be fed back and adjusted by detecting the power amplitude of the 54MHz fixed intermediate frequency signal.
The implementations described above are only some embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Claims (10)
1. A double-coupling double-mixing intermediate frequency signal power feedback circuit is characterized by comprising a first coupler, a second coupler, a first mixer, a second mixer, a first amplitude control unit, a second amplitude control unit, a voltage-controlled temperature compensation crystal oscillator, a digital step attenuator and a low-pass filter;
the coupling end of the first coupler is connected with the input end of the first amplitude control unit, the output end of the first amplitude control unit is connected with the local oscillator port of the first frequency mixer, the voltage-controlled temperature compensation crystal oscillator is connected with the intermediate frequency port of the first frequency mixer, the radio frequency port of the first frequency mixer is connected with the input end of the second amplitude control unit, and the output end of the second amplitude control unit is connected with the local oscillator port of the second frequency mixer;
the direct connection end of the first coupler is connected with the input end of the digital step attenuator, the output end of the digital step attenuator is connected with the input end of the second coupler, the coupling end of the second coupler is connected with the radio frequency port of the second mixer, and the intermediate frequency port of the second mixer is connected with the input port of the low-pass filter.
2. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 1, wherein a radio frequency signal is input from the input port of the first coupler, and the coupled port of the first coupler outputs a radio frequency input coupled signal; the radio frequency input coupling signal is regulated and controlled by the first amplitude control unit and then input to a local oscillator port of the first frequency mixer, and a crystal oscillator signal generated by the voltage-controlled temperature compensation crystal oscillator is input to an intermediate frequency port of the first frequency mixer; the first frequency mixer up-converts signals of a local oscillator port and an intermediate frequency port of the first frequency mixer and outputs the signals from a radio frequency port; the second amplitude control unit regulates and controls the output signal of the radio frequency port of the first frequency mixer and then inputs the regulated and controlled output signal to the local oscillation port of the second frequency mixer;
the digital step attenuator performs power attenuation regulation and control on a through port signal of the first coupler; the signal after attenuation regulation is input to an input port of the second coupler, one part of radio frequency signal is directly output from a through port of the second coupler, and the other part of radio frequency signal is coupled and output from a coupling port of the second coupler to obtain a radio frequency output coupling signal; the radio frequency output coupling signal is input to a radio frequency port of a second mixer, and the second mixer performs down-conversion on signals of a local oscillator port and the radio frequency port of the second mixer and outputs the signals from the intermediate frequency port; and the low-pass filter filters the output signal of the intermediate frequency port of the second mixer to obtain a final intermediate frequency signal.
3. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 1, wherein the first amplitude control unit is a first gain module; the second amplitude control unit comprises a second gain module and a resistance type attenuation network which are cascaded.
4. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 3, wherein said resistive attenuation network is connected in pi-type by three chip resistors.
5. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 3, wherein the first gain block and the second gain block are of the same type.
6. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 1, wherein the controllable attenuation of the digital step attenuator is 31.5dB, and the step is 0.5 dB.
7. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 1, wherein the low pass filter is a patch filter, the insertion loss for 54MHz intermediate frequency signals is around 0.33dB, and the out-of-band rejection for 2-4 GHz radio frequency signals is greater than 42 dBc.
8. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 1, wherein the frequency of the radio frequency signal is 2 GHz-4 GHz, and the frequency of the intermediate frequency signal is 54 MHz.
9. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 1, wherein the first coupler and the second coupler are the same type.
10. The double-coupled double-mixing intermediate frequency signal power feedback circuit according to claim 1, wherein the first mixer and the second mixer are the same type.
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