CN211656127U

CN211656127U - Frequency discriminator

Info

Publication number: CN211656127U
Application number: CN202020501115.XU
Authority: CN
Inventors: 崔建国; 宁永香; 崔建峰; 崔燚; 李光序
Original assignee: Shanxi Institute of Technology
Current assignee: Shanxi Institute of Technology
Priority date: 2020-04-08
Filing date: 2020-04-08
Publication date: 2020-10-09
Anticipated expiration: 2030-04-08

Abstract

The utility model discloses a frequency discriminator technology, which comprises a random signal input circuit, a random signal end diode pump circuit, a reference capacitor discharge circuit, a reference capacitor circuit, a reference voltage forming circuit, a reference capacitor charging circuit, a voltage-controlled oscillator end diode pump circuit, a voltage-controlled oscillator signal input circuit and a voltage-controlled oscillator circuit; the random signal f1 terminal pump circuit provides a discharge channel for the reference capacitor C1, and the voltage-controlled oscillator f2 terminal pump circuit provides a charging condition for the reference capacitor C1. The result of the simultaneous action of the two pump circuits is the result of the comparison of the two input signal frequencies f1 and f2, the capacitance C1 level generated by the comparison of the two frequencies is the reference level to be provided by the frequency comparator to the external circuit, the external circuit is the voltage-controlled oscillator itself, and the reference voltage controls the voltage-controlled oscillator to make the oscillation frequency closely follow the random input signal frequency.

Description

Frequency discriminator

Technical Field

The utility model relates to a technique of frequency discriminator, especially a frequency discriminator circuit who is different from traditional AFC circuit structure, a reference voltage value is exported to this kind of frequency discriminator, and this reference voltage will control voltage controlled oscillator, makes its oscillating frequency closely follow random input signal frequency.

Background

In a general circuit design, it is not difficult to obtain an oscillating signal with a certain fixed frequency, and if it is desired to modify the oscillating frequency of the circuit, it is usually achieved by modifying the time parameter τ of the rc network of the circuit, τ = R × C, so that the time parameter τ can be changed by modifying the resistance value, and the time parameter τ can also be modified by modifying the capacitance.

This method of adjusting the oscillation frequency is not practical in practical industrial control, for example, in the field of automation control, it is inconvenient to adjust the frequency of the output signal by modifying a certain capacitance or resistance value, because the control or controlled parameter in industrial automatic control is usually a voltage value or a current value, so that the adjustment of the oscillation frequency can be realized by using a voltage-controlled oscillator.

A voltage controlled oscillator is an oscillator in which an output frequency corresponds to an input control Voltage (VCO), and the oscillation frequency is a function of the input signal voltage, and the operating state of the oscillator or the parameters of the elements of the oscillation circuit are controlled by the input control voltage, thereby forming a voltage controlled oscillator.

If the requirement for stability of the oscillation frequency of the voltage-controlled oscillator is high, the voltage-controlled oscillator can be controlled by a frequency discriminator, the frequency discriminator is a circuit with output voltage corresponding to the input signal frequency, the input signal frequency is compared with a fixed reference frequency in a simple description, the output voltage of the comparator is the output voltage of the frequency discriminator, and the voltage value is fed back to control the VCO circuit to adjust the oscillation frequency of the VCO.

In the theory of automatic control systems, there is a case where it is desired that the frequency of the output signal of the voltage-controlled oscillator circuit must synchronously track the frequency of an input signal, but the frequency of the input signal is not constant as the reference frequency described above but varies randomly.

A frequency comparator circuit can be designed whose output voltage value will be a function of the random input signal frequency and the frequency of the voltage controlled oscillator, and if the comparator output voltage value is exactly the desired reference value (+ 6V) indicating that the oscillation frequency of the voltage controlled oscillator has closely tracked the input signal frequency, and if the voltage value deviates from the reference voltage value, the voltage value will be introduced into the control terminal of the voltage controlled oscillator, the oscillator can be automatically frequency controlled or tracked so that its oscillation frequency is consistent with the random input signal frequency at the other terminal.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a frequency discriminator circuit different from conventional design, which has simple structure and reliable use.

In order to achieve the above object, the present invention provides a frequency discriminator apparatus, which includes a random signal input circuit, a random signal terminal diode pump circuit, a reference capacitance discharge circuit, a reference capacitance circuit, a static reference voltage forming circuit, a reference capacitance charging circuit, a voltage controlled oscillator terminal diode pump circuit, a voltage controlled oscillator signal input circuit, a voltage controlled oscillator circuit; the random signal input circuit is composed of a coupling capacitor C01, a resistor R01 and a resistor R1, and random input signals are inputf ₁The capacitor C01 and the resistor R1 enter the diode pump circuit at the random signal end in sequence, and the connection point of the capacitor C01 and the resistor R1 is connected with a working ground through the resistor R01; the random signal end diode pump circuit is composed of a resistor R2, a transistor T1, a capacitor C2 and a diode D1, the right end of the resistor R1 is connected with the base of a transistor T1, 12V power supply is connected with a working ground through a resistor R2 and a C-E electrode of a transistor T1 in sequence, the collector of the transistor T1 is simultaneously connected with the anode of the diode D1 and the emitter of the transistor T2 through a capacitor C2, and the cathode of the diode D1 is connected with the working ground; the reference capacitor discharge circuit is composed of a transistor T2, a base electrode of the transistor T2 is connected with an operating ground, and a collector electrode of the transistor T2The anode of the reference capacitor circuit C1 is connected, and the cathode of the capacitor C1 is connected with the working ground; the 12V power supply is connected and operated sequentially through resistors R3 and R4 to form the static reference voltage forming circuit, the connection point of the resistors R3 and R4 is connected with the anode of a capacitor C1, and the anode of a capacitor C1 outputs a reference voltage U_C(ii) a The voltage-controlled oscillator signal input circuit is composed of a capacitor C02, a resistor R6 and a resistor R02, and the output signal of the voltage-controlled oscillator circuit VCOf ₂The voltage-controlled oscillator end diode pump circuit sequentially enters a capacitor C02 and a resistor R6, and the connection point of the capacitor C02 and the resistor R6 is connected with a power supply 12V through a resistor R02; the voltage-controlled oscillator end diode pump circuit is composed of a transistor T4, a resistor R5, a capacitor C3 and a diode D2, the left end of the resistor R6 is connected with the base of a transistor T4, 12V power supply is connected with a working ground through a resistor R5 and a C-E pole of a transistor T4 in sequence, the collector of the transistor is simultaneously connected with the cathode of a diode D2 and the emitter of the transistor T3 through the capacitor C3, and the anode of the diode D2 is connected with the working ground; the transistor T3 constitutes the reference capacitor charging circuit, and the collector of the transistor T3 is connected to the positive electrode of the capacitor C1.

The reference capacitor circuit C₁The level U being charged by charging and discharging at the same time_CAn input terminal U connected to the VCO of the voltage controlled oscillator circuit_C。

Drawings

Fig. 1 and 2 are included to provide a further understanding of the present invention and form a part of the present application, and fig. 1 is a schematic diagram of a frequency comparator circuit. Fig. 2 is an LC voltage controlled oscillator schematic circuit.

Detailed Description

Frequency comparator circuit

In the frequency comparator circuit described herein, we desire the reference voltage U_CCan be derived from random input signal frequenciesf ₁And the frequency of the voltage controlled oscillatorf ₂The electrical principle is shown in fig. 1 by comparison.

As can be seen from fig. 1, the frequency comparator circuit includes a random signal input circuit, a random signal terminal diode pump circuit, a reference capacitance discharge circuit, a reference capacitance circuit, a static reference voltage forming circuit, a reference capacitance charging circuit, a voltage-controlled oscillator terminal diode pump circuit, a voltage-controlled oscillator signal input circuit, and the like.

The basic principle of the design is briefly described as follows: the frequency comparator circuit has two input signalsf ₁、f ₂And the comparator circuit will compare the two input signals, randomly inputting the signalsf ₁Through an input capacitance C₀₁Resistance R₀₁、R₁Entering a frequency comparator circuit, and enabling the random signal to pass through a random signal end diode pump circuit and a reference capacitor discharge circuit to enable a reference capacitor C₁Partial discharge; and the voltage controlled oscillator outputs a signalf ₂Through an input capacitance C₀₂Resistance R₀₂、R₆And at the same time, the signal enters a frequency comparator circuit,f ₂the signal passes through a voltage-controlled oscillator terminal diode pump circuit and a static reference voltage forming circuit (namely R)₃、R₄) Reference capacitor charging circuit for charging reference capacitor C₁Charging realizes the prevention of the reference capacitor C₁The purpose of the discharge.

So that this reference capacitance C₁The average charge on (i.e. the desired reference voltage) will be the two input signalsf ₁、f ₂The reference voltage being a function of frequency and the two input signalsf ₁、f ₂The result of the frequency comparison will reflect the two input signalsf ₁、f ₂Whether the frequencies are equal.

In the quiescent state, i.e. when no signal is input to both input terminals, the transistor T₂、T₃All are turned off, and the power supply 12V passes through the voltage dividing resistor R₃、R₄Reference capacitor C of voltage divider pair₁Charging to half the supply voltage, i.e. 6V.

Function of diode pump circuit at random signal end

Upon application of a random signal to the transistor T₁The amplitude of the random signal is sufficient to be T₁Providing a turn-on voltage, T₁Collector-emitter ofElectrode conduction, T₁Is suddenly inverted to a "0" level, which will be driven by the capacitor C based on the property that the voltage across the capacitor cannot suddenly change₂Diode D₁The circuit being converted into a negative pulse trigger signal, i.e. capacitor C₂Right-hand side potential of or diode D₁Note that the positive pole is inverted from 0V to a negative trigger pulse less than "0" (instantaneous value about-12V).

With followingf ₁The instantaneous value of the random signal constantly changing, the transistor T₁Will be constantly on and off at the frequency of the incoming random signal, so the transistor T can generally be turned on and off₁、T₁Collector bias resistor R₂And a coupling capacitor C₂Discharge diode D₁The resulting circuit is visually referred to as a "diode pump circuit".

This circuit is named "pump circuit" because of its effect on the transistor T₂Generates a series of trigger negative pulses corresponding to the frequency of the input random signal, which are used to control the transistor T₂Is conducted to the collector upon T₂When the reference capacitor is turned on, the stored charge of the reference capacitor will pass through T₂、D₁Discharge with followingf ₁The next pulse of the signal arrives, the reference capacitor C₁And then according to the input end againf ₁The frequency of the signal is discharged in pulses, of course C₁There is a possibility of complete discharge.

Therefore, it isf ₁The exact function of the terminal diode pump circuit is as a reference capacitor C₁Provides a discharge path.

Function of voltage-controlled oscillator end diode pump circuit

Since the vco end circuits have different structures and different device types, the vco end diode pump circuits have different functions from the random signal end diode pump circuits. The voltage-controlled oscillator end diode pump circuit consists of a transistor T₄、T₄Collector bias resistor R₅And a coupling capacitor C₃Charging diode D₂And (4) forming.

The voltage-controlled oscillator signal passes through the diode pump circuit at the end of the voltage-controlled oscillator and is transmitted to the transistor T₃The emitter terminal of (2) also generates a series of ANDf ₂A trigger pulse signal corresponding to the frequency of the input signal, but not withf ₁The difference between the diode pump circuits is that the instantaneous value of the train of trigger pulses is approximately 2 times the supply voltagef ₁The instantaneous value of the trigger pulse of the end diode pump circuit is approximately equal to 1 times the negative supply voltage, the principle being briefly discussed as follows:

andf ₁end diode pump circuit analysis methods are similar, voltage controlled oscillator signalsf ₂To the transistor T₄High level signal of base electrode makes T₄On, the capacitance C₃The right end of the power supply is 0V, and a 12V power supply passes through a diode D₂Transistor T₄C-E of (C) is a capacitor C₃And (4) positive charging.

When voltage controlled oscillatorf ₂When the signal is inverted to a low level, the transistor T₄Cut-off, T₄The collector rises to 12V, and the capacitor C is based on the characteristic that the voltage at the capacitor cannot change suddenly and the characteristic of one-way conductivity of the diode₃The left-hand potential of the switch is reversed to a potential of about +24V,

therefore, withf ₂The instantaneous value of the signal is continuously changed, and the signal passes through a diode pump circuit at the end of the voltage-controlled oscillator and is transmitted to a transistor T₃The emitter terminal of (2) also generates a series of ANDf ₂The instantaneous power supply voltage corresponding to 2 times of the input signal frequency triggers a pulse signal.

The 2-time instantaneous power supply voltage trigger pulse signal is used to control the transistor T₃Is in a conducting state, the above-mentioned 24V transient trigger pulse will try to be the reference capacitance C₁And (6) charging.

Thus, the following is finally realized: with followingf ₂A series of pulses of the signal comes in,f ₂the end diode pump circuit is corresponding tof ₂The frequency of the input signal is in short pulses to the reference capacitor C₁And (6) charging.

Therefore, it isf ₂The end diode pump circuit is used as a reference capacitor C₁Providing charging conditions.

Reference voltage formation and its use in frequency tracking

f ₁End pump circuit as reference capacitor C₁Providing a discharge channel,f ₂End pump circuit as reference capacitor C₁A charging channel is provided.

The two above "pump circuits" act simultaneously, with the end result that: reference capacitance C₁The level obtained by charging and discharging at the same time is obtained byf ₁、f ₂The result of the frequency comparison of the two input signals is the reference level that the frequency comparator is intended to provide to the external circuitry (in this design the external circuitry is referred to as the voltage controlled oscillator itself), which will control the voltage controlled oscillator to modify the oscillation frequency to track the random input signalf ₁Until the frequencies are equal, which is the result we finally expect, the frequency tracking procedure is briefly described below.

It is obvious that if two input signals are providedf ₁、f ₂The same frequency, the reference capacitor C in each period₁The amount of charge and discharge is also equal, so that C is present₁Voltage U across_CShould equal half the supply voltage (6V) if the signal is randomly inputf ₁Is lower than the input signal of the voltage-controlled oscillator terminalf ₂Frequency of (C)₁Reference voltage U of end output_CWill be below 6V; if it isf ₁At a higher signal frequency thanf ₂The signal frequency of (1), the output reference voltage U_CWill be higher than 6V.

The frequency comparator of the circuit can also be called a frequency discriminator actually, and can be used in the occasions with higher requirement on the stability of the frequency or needing to carry out automatic adjustment on a certain frequency if the reference voltage U is used_CIs led back tof ₂The end voltage-controlled oscillator can be subjected to Automatic Frequency Control (AFC) to make its frequency and another end（f ₁End) to realize the tracking of the signal frequency.

Voltage controlled oscillator

The types of Voltage Controlled Oscillators (VCO) are generally three, namely an LC voltage controlled oscillator, an RC voltage controlled oscillator and a crystal voltage controlled oscillator, wherein the frequency stability of the RC voltage controlled oscillator is low and the frequency modulation range is wide; the frequency stability of the crystal voltage-controlled oscillator is high, but the frequency modulation range is narrow; and the LC voltage-controlled oscillator is arranged between the two.

In the present frequency comparator circuit, the LC voltage-controlled oscillator is taken as an example and describedf ₂The end voltage controlled oscillator realizes a circuit for controlling oscillation frequency by reference voltage.

In any LC voltage controlled oscillator circuit, an LC voltage controlled oscillator can be formed by connecting a voltage controlled variable reactance element to an oscillator circuit, except that the voltage controlled variable reactance element in the early stage is a reactance tube, and most of the latter uses a varactor diode.

Fig. 2 shows an electric operating principle circuit of the krasplat type LC voltage-controlled oscillator. In the figure, T is a transistor, L is a loop inductance, C₁、C₂、C_VIs a loop capacitance, C_VThe capacitance exhibited by the varactor when reverse biased; usual capacitance C₁、C₂Ratio C_VMuch larger. When the VCO inputs the control voltageU _CWhen changed, C_VAnd changes accordingly, the oscillation frequency is changed. The relationship between the output frequency and the input control voltage of the voltage-controlled oscillator is

Figure DEST_PATH_394055DEST_PATH_IMAGE001

In the formula C₀The capacitance of the varactor diode at zero reverse bias; phi is the junction voltage of the varactor; gamma is an index of junction capacitance change, and in practical use, various compensation measures can be taken in order to obtain a linear control characteristic.

In fact, the frequency comparator described herein is also essentially a "frequency discriminator" except that the reference frequency is changed from a fixed frequency to a random frequency, and the output reference voltage value of the comparator is fed back to control the oscillation frequency of the voltage-controlled oscillator, thereby closely tracking the frequency of the random signal, and thus also belonging to an "AFC".

Claims

1. A frequency discriminator is characterized by comprising a random signal input circuit, a random signal end diode pump circuit, a reference capacitor discharge circuit, a reference capacitor circuit, a static reference voltage forming circuit, a reference capacitor charging circuit, a voltage-controlled oscillator end diode pump circuit, a voltage-controlled oscillator signal input circuit and a voltage-controlled oscillator circuit; the random signal input circuit is composed of a coupling capacitor C01, a resistor R01 and a resistor R1, and random input signals are inputf ₁The capacitor C01 and the resistor R1 enter the diode pump circuit at the random signal end in sequence, and the connection point of the capacitor C01 and the resistor R1 is connected with a working ground through the resistor R01; the random signal end diode pump circuit is composed of a resistor R2, a transistor T1, a capacitor C2 and a diode D1, the right end of the resistor R1 is connected with the base of a transistor T1, 12V power supply is connected with a working ground through a resistor R2 and a C-E electrode of a transistor T1 in sequence, the collector of the transistor T1 is simultaneously connected with the anode of the diode D1 and the emitter of the transistor T2 through a capacitor C2, and the cathode of the diode D1 is connected with the working ground; the reference capacitor discharge circuit is composed of a transistor T2, the base electrode of the transistor T2 is connected with an operating ground, the collector electrode of T2 is connected with the anode of the reference capacitor circuit C1, and the cathode of the capacitor C1 is connected with the operating ground; the 12V power supply is connected and operated sequentially through resistors R3 and R4 to form the static reference voltage forming circuit, the connection point of the resistors R3 and R4 is connected with the anode of a capacitor C1, and the anode of a capacitor C1 outputs a reference voltage U_C(ii) a The voltage-controlled oscillator signal input circuit is composed of a capacitor C02, a resistor R6 and a resistor R02, and the output signal of the voltage-controlled oscillator circuit VCOf ₂The voltage-controlled oscillator end diode pump circuit sequentially enters a capacitor C02 and a resistor R6, and the connection point of the capacitor C02 and the resistor R6 is connected with a power supply 12V through a resistor R02; the voltage-controlled oscillator end diode pump circuit is composed of a transistor T4, a resistor R5, a capacitor C3 and a diode D2, the left end of the resistor R6 is connected with the base electrode of a transistor T4, and 12V power supply sequentially passes through a resistor R5 and a C-E electrode of a transistor T4The collector of the transistor is connected with the cathode of the diode D2 and the emitter of the transistor T3 at the same time through the capacitor C3, and the anode of the diode D2 is connected with the working ground; the transistor T3 constitutes the reference capacitor charging circuit, and the collector of the transistor T3 is connected to the positive electrode of the capacitor C1.

2. A frequency discriminator according to claim 1, wherein: the reference capacitor circuit C₁The level U being charged by charging and discharging at the same time_CAn input terminal U connected to the VCO of the voltage controlled oscillator circuit_C。