Transformation principle of voltage and frequency

chart 3.3.17
XTR1I0 Basic application circuit
3.4 voltage / Rate transformation and frequency / Voltage conversion
3.4.1 voltage / Frequency conversion
Voltage sequence conversion (UFCO) It can transform the input signal voltage into the corresponding frequency signal , That is, its output signal frequency
The rate is proportional to the voltage value of the input signal , This provides a simple Analog to digital conversion method . Do this kind of transformation
The reason is to transmit and decode a pulse train , It is much more accurate than an analog signal , Especially when the transmission line is long
Or in case of serious interference . voltage / The application of frequency conversion circuit is very extensive , In different application fields
Different names : In radio technology , It is called frequency modulation (FM): In the signal source circuit , It is called pressure control
oscillator (UCO); In signal processing and transformation circuit , It is called voltage / Frequency conversion circuit or quasi mode / Digital conversion electricity
road .
Integrate the complex prototype voltage / The frequency converter consists of an integrator 、 It is composed of comparator and integral recovery analog switch . Various
Integrate the complex prototype voltage / The working principle of frequency converter is basically similar , The main difference lies in the reset method 、 Long reset time
Short different . Its analog switch is usually transistor 、 FET and other components . Pictured 3.4.1 The integrated complex prototype voltage is shown / frequency
Schematic diagram of the converter .
An analog switch comes out of the input signal !
↑ Reference voltage Ka
chart 3.4.1 integral Recovery voltage / Schematic diagram of frequency converter
Integrate the complex prototype voltage / The working principle of the frequency converter is : Input signal ui Integral by integrator , Electricity after integration
Pressure
Pressure uo And the reference voltage of the comparator HR Compare , When 146=711 when , Comparator flip , Its output controls the analog switch to switch
Switch to w:
The analog switch resets the integrator to zero .
Assume ur>0, Then the integrator output is
u.=
fu.dr
(3-4-1)
In style ,r Is the time constant of the integrator .
After a period of time T after ,u,=-uT=up, Comparator flip , Integrator after a period of time T2 Then it reverts to
zero . When designing circuits, make T2<<T, Then the output frequency of the comparator is
1
11
fo =
T+T2 T TUle
One 1
(3-4-2)
≈
The output frequency of the circuit fo With input signals u; Is proportional to the amplitude of .
Composed of general analog integrated circuits UFC circuit , Especially the special analog integrated voltage / Frequency converter , Its performance
Stable 、 High sensitivity 、 Small nonlinear error .
Integrated complex prototype voltage composed of integrated operational amplifier / The accuracy and dynamic range of the frequency converter and its output waveform integral complex prototype voltage ratio converter are limited by the nonlinear characteristics of the reset circuit
system , The main method to improve its accuracy is to shorten the reset time . To make its nonlinear error from 0.1% Increase a quantity
level , achieve 0.01%, Then the reset time must be reduced to the minimum signal period 0.01% following . When the rated working frequency is
10kHz when , The minimum period of the signal is 0.1ms, The reset time must be less than 0.01μs, Make the integral complex prototype voltage / frequency
Converters are often difficult to implement . The charge balance method can solve the above problems . Pictured 3.4.4、 chart 3.4.5 Charge shown
Balanced voltage / Schematic diagram and waveform diagram of frequency converter . The reset circuit of the converter consists of a timing circuit 、 Constant current source and mode
The proposed switch consists of , The reset circuit works by the comparator A2 control . Whenever the output of the comparator changes from high potential to low potential
when , The output pulse width of the timing circuit is fixed as T2 Negative pulse , send VD2 end ,VD1 Conduction . Input current I Join in
after , integrator A Negative integral , When A: The output voltage drops to the comparator A2 Given reference voltage up when , The comparator
A2 The output of is changed from high potential to low potential , So the reset circuit takes the fixed amount of charge from the integrating capacitor 1I2. because I
It is always larger than the heart, so during the negative pulse output of the timing circuit , Integrator forward integration , Until the timing circuit is restored , Just open again
Start the next cycle . In a cycle , The amount of charge obtained by integrating the capacitance should be equal to the amount of charge released , namely 1T=
IJI2, Then the output frequency is