SU1370618A1 - Converter of modulation depth value of amplitude-modulated signal to digital code - Google Patents

Description

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The invention relates to a measurement technique and can be used to measure the modulation depth of amplitude-modulated (AM) signals, the envelope of which lies in the range of low and infra-low frequencies.

The purpose of the invention is to increase the speed and expand the functional capabilities of the converter by providing a measurement time setting that is a multiple of the envelope period of the input AM signal.

FIG. 1 shows a functional converter circuit; figure 2 - timing charts of his work.

The converter contains an input signal amplifier 1, a synchronous demodulator 2 AM signal, a control voltage driver 3, a synchronous indicator 4 of the AM signal envelope, a triangular voltage generator 5, the period of which is much less than the period of the AM signal envelope, the first 6, the second 7 and the third 8 comparators, the first 9, the second 10 and the third 11 keys, the generator 12 of the reference frequency, the first 13 and the second 14 counters, the RS flip-flop 15, the inverter 16, the OR element 17, the arithmetic unit 18 and the sensor 19 of the measuring mode input of amplifier 1 is input AM c drove Uj (t), and the output is connected to the first signal input of the synchronous demodulator {) a 2 and through the control voltage generator 3 with its second (control) input and the first input of the measuring mode setting unit 19 the first output of the synchronous demodulator 2 is connected to the second input of the measurement mode setting device 19 and through the synchronous rectifier 4 of the AM signal envelope to the first inputs of the first 6 and third 8 comparators, to the first input of the RS flip-flop 15 and through the inverter 16 to its second input, the second output of the synchronous demodulator 2 connected to the first entrance torogo comparator 7, the second input of the first komla50

The rator 6 is connected to the first (inverse) output of the generator 5 of a triangular voltage, and the second inputs of the comparators 7 and 8 are connected to its second (direct) output, the outputs of the comparators 6-8 are connected respectively to the first inputs of the keys 9-11, the first output The measurement mode setting unit 19 is connected to a third (control) input.

Q

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0 5 0 5 0

0

with

synchronous demodulator 2, and the second output with the second inputs of keys 9-11, the third inputs connected to the output of the reference frequency generator 12, the output of the first key connected to the first input of the element OR 17, the second input connected to the output of the third key 11, and the output to the input of the second counter 14, the output of the second key 10 through the first counter is connected to the first input of the arithmetic unit 18, the second input connected to the output of the second counter 14, and the third input to the output of the RS flip-flop 15.

The synchronous demodulator 2 contains (an example of execution) the keys 20 and 21, the integrators 22 to 23, the differential amplifier 24 and the storage unit 25, the output of the differential amplifier 24 through the normally open key 21 and the storage unit 25 connected to the second input of the integrator 22, the control inputs of the keys 20 and 21 are connected to the second and third (control) inputs of demodulator 2.

The mode setting unit 19 contains (example of execution) the first 26 and second 27 frequency dividers, the first

28 and second 29 decoders, limiting amplifier 30, driver

The 31 sampling period codes and the measurement time code generator 32, the first input of the measurement mode setting unit 19 is connected via a frequency divider 26 and the decoder 28 to its first output, while the second input of the decoder 28 is connected to the output of the sampling period code generator 31, and the second input of the setting unit 19 measurement mode through the amplifier-limiter 30, frequency divider 27

and the decoder 29 is connected to its second output, and the second input of the decoder

29connected to shaper output

32 codes of measurement time.

Synchronous demodulator 2 (FIG. 1) is an interpolating filter that realizes the recovery of a continuous function (the envelope of the AM signal) from its discrete samples.

The device works as follows.

To the input, amplifier 1 is supplied by an AM signal of the type of FIG. 2a)

U6x (t) V (1 + m sinQ t) sin LO t, (1)

where V is the amplitude of the unmodulated carrier voltage; ) rf is the carrier angular frequency; ) P - angular frequency of the envelope; ,

m is the modulation coefficient. The voltage K, Uj (t) is fed to the signal input of the demodulator 2 (K, is the transfer coefficient of the amplifier 1).

At the output of the former 3, square-shaped pulses of frequency f with fronts corresponding to the moments of crossing the carrier voltage across the zero (Fig. 26), are received at the second (control) input of the demodule (torus 2 and the divider input). 26 setting frequency 19.

As a result of a one-by-one comparison of the output signal of the frequency divider 26 with the output of the generator 31, rectangular pulses are generated at the output 20 of the decipher 28 following the period (Fig. 2b)

(2)

T Kjj,

25

where K 2 is the division ratio specified by the shaper 31.

The rectangular pulses, which come through the second input of the modulator 2 to the control input of the switch 20, open it at time intervals corresponding to, for example, the positive half-waves of the input AM signal. The low-pass filtering of the signal formed at the output of the switch 20, and the filling of the envelope of the frequency F from it, consist in its twofold integration at each sampling period Ta by the integrators 22 to 23 to the feedback voltage from the output of the differential amplifier

24 through key 21 and a storage unit

25 to the second input of the integrator 22.

As a result, a voltage is formed at the output of the integrator 23, which contains the envelope of the input AM signal and a constant component proportional to the carrier level (Figure 2d):

Uj U) K, K (mV t + V), (3)

where K is the transmission coefficient of the path input of the key 20 is the output of the integrator 23.

Simultaneously with low-frequency filtering, the first derivative of the signal (3) is generated at the output of the integrator 22 (FIG. 2d)

and, (t) K /, K4mV cosP t.

(M

,

Q h

0 5

about Q

where K is the transmission coefficient of the path input of the key 20 is the output of the integrator 22.

In contrast to analog low-pass filters, interpolating filters that realize the recovery of a continuous function from its discrete samples provide high accuracy and speed. When choosing a sampling frequency of 6 times the upper relative envelope frequency, the level of high-frequency sampling noise does not exceed 1%. Here, the transients end in two sampling periods.

The voltage (4) through the limiting amplifier 30 and the frequency divider 27 is supplied to the first input of the decoder 29. As a result of a comparison of the output signal of the frequency divider 27 with the code of the driver 32, rectangular pulses are generated at the output of the decoder 29, the duration of which is a multiple of the AM envelope period signal (for example, fige):

t PT, (5)

where n

1, 2, 3, 1

T

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five

At the same time, the voltage (4) is fed to the signal input of the synchronous well terminal 4, the control input of which is supplied by the reference voltage

and „„ (t) J, r.os (fl t -i-v). (6)

As a result, a signal is formed at the output of the synchronous rectifier 4 (FIG. 2g)

U (t) K, conforming t I, (7)

moreover, U (t) 70 at U (t) 0 at v.

The voltage (7) goes to the first inputs of the comparators 6 and 8, and the voltage (3) to the first input of the comparator 7. The voltages (G) and (7) are compared with the output voltage) and (t) of the generator 5 sawtooth tension

At the output of the comparator 7, the comparator 8 (at U4 (t) is 0) or the comparator 6 (at U4 (t) 0) rectangular pulses are formed, the duration of which corresponds to the time intervals when the instantaneous values

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the triangular voltage Uj (t) or U) j (t) is greater than U, (t) or U + (t) (Fig. 2e, and), respectively.

The duration of the pulses at the output of the comparator 7 is changed by the law

{, (t) - 0 (Urn t), (8)

and at the outputs of the comparator 6 (with

U4 (t): o) and comparator 8 (with

U4U) 0) - according to the law of JO

  r t sol t. (9) In expressions (8) and (9)

and - the amplitude of the triangular tension and d (t).

No. 4 pulses); (t) and. (t) In the time interval t defined by expression (5), open the keys 10 and 11 (with U4 (t) 7 o) and the key 9 (with U4 (t) 0).

If you choose, the number of triangular voltage periods laid down in the envelope period is equal to (RTD). Then the number of pulses N, the reference frequency f received through the switch 10 to the counter 13 during the time t is equal to

N, fo

(FT,) i 1

(12)

The number of frequency pulses fd received 9 or key 11 and the element time t is equal to

0.5 (FT,) N,

2f.

i 1

When Tf T d expression (12) and (13)

in view of (8) and (9), respectively, are reduced to the form:

N, f Jo, (t), K,

(I)

about

t /:

N, 2f, J t: (t), K, K, -. 5,

0, /

where K is the shape factor of the envelope. Thus, the code N ,, fixed by the counter 13, is proportional to

O

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five

30 5

0

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the constant component V of the voltage (G), and the NJ code, recorded by the counter 14, is proportional to the average direct value of the tM envelope.

The codes N and N are entered into the arithmetic unit 18, respectively, through its first and second inputs, and the third input receives a single or zero level of the output voltage — the output of the RS flip-flop 15, determined by the polarity formed by the synchronous voltage-rectifier 4 (7) and carrying information about the phase ratio of the AM input signal and the reference voltage. As a result of dividing (15) by (14) taking into account the voltage level on the RS-flip-flop voltage, the output of the arithmetic unit 18 generates a code proportional to the modulation factor of the input AM signal:

N (m),

where Kj is the proportionality coefficient. N (m) 7 O with N (m); Oh when

4 iT.

one

Thus, the conversion time of the proposed device does not exceed the period of the input AM signal by bending, which makes it possible to measure the parameters of signals limited in duration.

Claims (1)

Invention Formula The modulator of the amplitude-modulated signal to the digital code contains the input signal amplifier, the output is connected to the first BXO-I house of the synchronous demodulator of the amplitude-modulated signal and through the driver of the control voltage with the second input of the synchronous demodulator , a synchronous envelope meter, the first input connected to the first output of the synchronous demodulator, and the second input - to a source of reference voltage, a triangular voltage generator, the first and second outputs connected respectively to the first inputs of the first and second comparators, the third comparator, the first and second keys, the first inputs connected to the outputs of the first and second comparators, the second inputs to the output of the reference frequency generator, the output of the second key connected to the counter input, characterized in that , in order to increase speed and enhance functionality by providing a measurement time setting that is a multiple of the envelope of the input amplitude-modulated signal, measurement mode sensor, third key, second counter, arithmetic unit, RS trigger, inverter and OR element, the first input of the measurement mode setting unit being connected to the output of the control voltage driver, the second input to the first output of the synchronous demodulator, the first output the unit of measurement mode to the third input is a synchronous demodulator; the second output is to the third inputs of the first and second keys and the first input of the third key, the second input connected to the output the reference frequency generator, the second output of the synchronous demodulator is connected to the second input of the second comparator, the output of the synchronous uplink envelope is connected to the second inputs of the first and third comparators, to the first input of the RS flip-flop and through the inverter to its second input, the output of the first counter is connected to the first the input of the arithmetic unit, the output of the first key - with the first input of the element OR, the second input connected to the output of the third key, the third input of which is connected to the output of the third comparator, and the output of the element OR - with the input The second counter, connected to the second input of the arithmetic unit, the output of the RS flip-flop is connected to the third input of the arithmetic unit, and the second input of the third comparator is connected to the second output of the triangular voltage generator. 1pg | ppppppppppppppp raTVWMWeWe a, (t)   A dt  V  finnnnnnnnnnn.f V Fflflff a, (t)