RU2328068C1 - Amplitude demodulator - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention concerns radio engineering and can be applied in precision measurement instruments and in receivers for demodulation of amplitude-modulated signals. Amplitude demodulator (AD) includes two voltage level self-tuning rings. First self-tuning ring consists of adder unit (2) of peak value converter (PVC) (3), first selection and storage device (SSD) (4), first direct current amplifier (DCA) (5) and first low-frequency filter (6), and sustains precise stability of AD operation point. The second self-tuning ring consists of adder unit (2), PVC (3), second SSD (7), second low-frequency filter (8), second DCA (9), bleeder (10) and second switch (13), and sustains stable PVC (3) conversion factor at different levels of alternate voltage.

EFFECT: improved demodulation accuracy.

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Description

The invention relates to radio engineering and can be used in measuring technique and in receiving devices for demodulating signals modulated in amplitude.

A device is known according to USSR author's certificate SU No. 1566459 A1 H03D 1/18, comprising a first resistor, a first capacitor, a cathode of a first diode, a cathode of a second diode, a second capacitor, a second resistor, the connection point of the resistors being the input of the device, connected in series with the third and a fourth capacitors, the first connected to the connection point of the first resistor and capacitor, and the second to the connection point of the second resistor and capacitor, the alternating voltage amplifier connected in series I and the fifth capacitor, the inverting input of the amplifier connected to the connection point of the third and fourth capacitors, and the fifth capacitor to the connection point of the first and second diodes, the first integrating amplifier connected in series, the integration input of which is connected to the connection point of the first capacitor and diode and the third resistor, which is connected to the connection point of the second resistor and capacitor, the second integrating amplifier is connected in series, the inverting input of which is connected to the connection point the second capacitor and diode and the fourth resistor, which is connected to the connection point of the first resistor and capacitor.

Since the connection of the first resistor, the third capacitor, as well as the second resistor and the fourth capacitor with the input capacitance of the AC voltage amplifier form a low-pass filter, the bandwidth of this device at high frequencies is limited. Therefore, the disadvantage of this device is the limited range of operating frequencies.

Also known amplitude detector, described in the book of Volgin L.I. Measuring converters of alternating voltage. M., Sov. Radio, 1977, p.197, fig. 4.32, containing a series-connected high-pass filter consisting of a capacitor and a resistor, a switch, an amplitude value converter (PAZ), an isolation capacitor, a filter, an alternating voltage amplifier (UPN), a synchrodetector, a controlled divider voltage (UDN), the output of which is the output of the device and a voltage divider on resistors, the output of which is connected to the second input of the switch, as well as a control voltage generator, the outputs of which are connected to the control input of the comm Tatorey sync detector and a second input, and a reference voltage source coupled to the second input of the UDN.

If the amplitude of the envelope of the output PAZ signal is written as U _m -βE (see Volgin L.I. Measuring transducers of alternating voltage. M., Sov. Radio, 1977, p.197), where

U _m is the amplitude of the input signal,

β is the transfer coefficient of the voltage divider on the resistors,

E is the output constant voltage at the output of the amplitude detector, the conversion function of this amplitude detector can be written as follows (see Volgin L.I. Measuring transducers of alternating voltage. M., Sov. Radio, 1977, p.198, formula 4.41).

where k = k ₁ · k ₂ · k ₃ · k ₄ · k ₅ - the product of the transmission coefficients of the passive PAZ, filter, UPN, synchrodetector and UDN;

- функция, взаимообратная функции преобразования пассивного ПАЗ.

- function, reciprocal of the conversion function of the passive PAZ.

As can be seen from the above formula, the output voltage of this amplitude detector largely depends on the passive PAZ transmission coefficient, the operating point of which is not stabilized.

Therefore, at low temperature and low (50-100 mV) input signal level, the PAZ transmission coefficient is close to zero. Moreover, in accordance with the above formula, the amplitude detector will malfunction.

The closest analogue is the device described in the book of Volgin L.I. Measuring converters of alternating voltage. M., Sov. Radio, 1977, p.197, Fig.4.32, containing a switch, an amplitude converter, a voltage divider, a control voltage generator and a reference voltage source.

To improve the accuracy of converting the amplitude of the input variable signal to a constant voltage while maintaining the frequency range of the passive PAZ, an amplitude detector is proposed that contains a key, an amplitude value converter, a pulse generator, a reference voltage source, a voltage divider, characterized in that an adder connected between a key and a converter of amplitude values, connected in series with a first sampling and storage device, a first DC amplifier, a first filter p low frequencies, the output of the first sampling and storage device is connected to the inverse input of the first DC amplifier, and the output of the first low-pass filter is connected to the second input of the adder, the second sampling and storage device, the second low-pass filter, the second DC amplifier are connected in series, the output of which is the output of the device, as well as the second key, while the inverse output of the second DC amplifier through a voltage divider and the second key is connected to the third input of the adder, the direct output of the pulse generator is connected to the control inputs of the first and second keys and the second sampling and storage device, and the inverse output of the pulse generator is connected to the control input of the first sampling and storage device, the output of the reference voltage source is connected to the direct input of the first DC amplifier and to the inverse input second DC amplifier.

The drawing shows a diagram of the device and shows:

1 - the first key,

2 - adder

3 - Converter amplitude values,

4 - the first device of sampling and storage,

5 - the first DC amplifier,

6 - the first low-pass filter,

7 - a second device for fetching and storing,

8 - the second low-pass filter,

9 - second DC amplifier,

10 - voltage divider

11 - pulse generator

12 is a source of reference voltage

13 - the second key.

The amplitude detector contains: a first key 1, an adder 2, an amplitude value converter 3, a first sampling and storage device (UVX) 4, a first direct current amplifier (DCT) 5, a first low-pass filter (LPF) 6, a second sampling and storage device 7 , a second low-pass filter 8, a second DC amplifier 9, a voltage divider 10, a pulse generator 11, a reference voltage source (ION) 12, a second switch 13.

The amplitude detector operates as follows. From the direct output of the pulse generator 11, the signal is supplied to the control inputs of the first key 1, second key 13 and the second UVX 7, from the inverse output to the control input of the first UVX 4.

When there is no pulse at the inputs of the first key 1 and second key 13, the signals do not pass through them, i.e. the input alternating signal and the signal from the output of the voltage divider 10 do not arrive at the second and third inputs of the adder 2. At the same time, the output of the PAZ 3 contains a constant voltage accumulated on the internal capacitance, and the input from the output of the first low-pass filter 6 is cleaned from the input. The first UVX 4 at this point in time is open for sampling at the control input, and the second UVX 7 stores the previous state of the PAZ 3. The voltage from the output of UVX 7 is subtracted from the voltage of ION 12 and through the second CNT 9, the voltage divider 10 goes to the input of the second yucha 13.

At the time of the pulse, the first 1 and second 13 keys are opened from the pulse generator 11 and the signals from their outputs are fed to the inputs of the adder 2, and then through the PAZ 3 to the input of the first UVX 4, which is in the state of storage of the previous value of the input signal. The second UVX 7 at this moment is in the mode of sampling the signal from the output of the PAZ 3.

Thus, we have two auto-tuning rings of the signal amplitude acting alternately in time. The first consists of the adder 2, PAZ 3, the first UVX 4, the first UPT 5 and the first low-pass filter 6. The second of the adder 2, PAZ 3, the second UVX 7, the second low-pass filter 8, the second UPT 9, the voltage divider 10, the second switch 13.

The characteristic equation for the auto-tuning ring containing the adder 2, PAZ 3, the first UVX 4, the first UPT 5, the first low-pass filter 6 is as follows.

U _LPF1 = (U _ION -U _LPF1 · K _SUM · K _PAZ · K _UVX1 ) · K _UPT1 K _LPF1 ,

where U _ION is the voltage at the output of ION 12,

U _PAZ - voltage at the output of PAZ 3,

K _UVX1 - transmission coefficient of the first UVX 4,

K _LPF1 - the transmission coefficient of the first LPF 6,

U _LPF1 - voltage at the output of the first LPF 6,

K _SUM - the transfer coefficient of the adder 2,

K _UPT1 - transmission coefficient of the first CNT 5.

After the transformations we get.

U _LPF1 = (U _ION · K _UPT1 · K _LPF1 ) / (1 + K _SUM · K _PAZ · K _UVH1 · K _UPT1 · K _LPF1 )).

At K _LPF1 ≈1, K _SUM ≈1, K _UPT1 ≈50000, K _UVX1 ≈1, K _PAZ ≈0.01-0.05 we get

U _FNCH1 ≈U _ION / K _PAZ.

Those. at times when the first key 1 and the second key 13 are closed, the output of the first low-pass filter 6 contains a voltage equal to U _ION / K _PAZ .

Consider the work of the second auto-tuning ring, which consists of an adder 2, PAZ 3, a second UVX 7, a second low-pass filter 8, a second UPT 9, a voltage divider 10, and a second switch 13. The characteristic equation for this ring will look as follows.

U _OUT = ((U + U _{FNCH1 VC} · _K1 K -U _OUT · K · K _{Nam K2)} · K · _MSA · K K _{PAZ SHA2} · K -U _{FNCH2 ION)} · K _UPT2,

where U _BX - input alternating voltage,

U _LPF1 - voltage at the output of the first LPF 6,

U _OUT - voltage at the output of the amplitude detector,

K _DN - the transfer coefficient of the voltage divider 10,

K _UPT1 - transmission coefficient of the second UPT 9,

_K1 - key transfer ratio 1,

K _K2 - key transfer ratio 13.

Given that U _LPF1 ≈U _ION / K _PAZ , as well as K _K1 ≈K _K2 ≈1, K _SUM ≈1, K _UVX2 ≈1, K _LPF2 ≈1, and also that K _UPT2 ≈50000, K _PAZ ≈0.025 -0.5 after transformations we get.

U = U _{OUT VC} · K · K _{UPT2 PAZ} / (1 + K _dN · K · K _{UPT2 PAZ)} ≈U _VH / K _Nam.

Those. the voltage at the output of the described amplitude detector does not depend on the unstable transmission coefficient of PAZ 3, or on the change in voltage of the ION 12.

It should be noted that the stability of the transmission coefficients of all devices included in the amplitude detector is several times higher compared to the stability of a passive PAZ. Therefore, the inequality to the unit of coefficients K _K1 , K _K2 , K _SUM , K _UVX2 , K _{LPF2 is} easy to compensate for when setting the amplitude detector, and their influence on the stability of the transfer coefficient of the amplitude detector can be neglected in the future.

Thus, the auto-tuning ring, consisting of the adder 2, PAZ 3, the first UVX 4, the first UPT 5, the first low-pass filter 6 provides with high accuracy the stability of the working point of the amplitude detector, and the auto-tuning ring, consisting of the adder 2, PAZ 3, the second UVX 7 , the second low-pass filter 8, the second UPT 9, the voltage divider 10 and the second switch 13 provides stability of the conversion factor PAZ 3 for different levels of alternating voltage. All this significantly increases the accuracy of the conversion of the amplitude values of the variable signals relative to analogues.

The amplitude value converter (PAZ) can be implemented according to one or two-diode circuits or using a transistor in a diode inclusion. The adder can be made on resistors or on a broadband transformer. The sampling and storage device in the simplest case is a key whose output is connected to a storage capacitor, the second end of which is connected to a common wire. The remaining elements of the device can be performed on a standard element base and do not have any features.

Claims (1)

An amplitude detector containing a key, an amplitude value converter, a pulse generator, a reference voltage source, a voltage divider, characterized in that an adder is connected thereto, connected between the key and the amplitude value converter, a first sampling and storage device, a first DC amplifier connected in series, the first low-pass filter, the output of the first sampling and storage device is connected to the inverse input of the first DC amplifier, and the output of the first filter is low the frequency is connected to the second input of the adder, a second sampling and storage device, a second low-pass filter, a second DC amplifier, the output of which is the output of the device, and a second switch, the inverse output of the second DC amplifier through a voltage divider and a second switch connected to the third input of the adder, the direct output of the pulse generator is connected to the control inputs of the first and second keys and the second device for fetching and storing, and the inverse output of the generator is pulse control connected to the input of the first sampling device and the storage reference voltage source output is connected to the direct input of the first DC amplifier and to the inverse input of the second amplifier is DC.