SU1379750A1 - Converter for modulation factor value of amplitude-modulated signal - Google Patents

Abstract

The invention can be used to measure the modulation depth of amplitude modulated (AM) signals. The purpose of the invention is to simplify the converter and increase noise immunity. The converter contains a synchronous demodulator 2 AM signals, a shaper 3 control voltages, a rectifier 4 of the envelope AM signals, comparators 5 and 6, keys 8, 9, 13-16, a shaper 10 commands, an indicator unit 11, setpoint Measurement mode 12 and integrators 17 and 18. A comparator 7, inverters 19 and 20, element 21 are entered into the converter, and new functional connections are formed. Therefore, the transmission coefficient of the comparator 6 on the second input determines the ET-dead zone of the converter according to the modulation coefficient it converts, independent of the carrier level of the input signal. 2 Il. i 1 (L CA9 M

Description

. f

one

The invention relates to a measurement technique and can be used to measure the modulation depth of amplitude modulated (AM) signals.

The purpose of the invention is to simplify the device and increase the noise: stability.

FIG. 1 shows a functional diagram of the converter; in fig. 2 - time diagrams of his work.

The converter contains an input signal amplifier 1, a synchronous demodulator 2 AM signals, a control voltage driver 3, a rectifier 4 AM signals, the first, second and third comparators 5-7, the fifth and fourth switches 8 and 9 , the command driver 10, the indicator unit 11, the measurement mode setting unit 12, the first, second, sixth and third keys 13-16, the first and second integrators 17 and 18, the first and second inverters 19 and 20, and element 21.

The measurement mode setting unit 12 comprises first and second frequency dividers 22 and 23, first and second decoders 24 and 25, limiter amplifier 26, sampling period code generator 27 and measurement time code generator 28. Synchronous demodulator 2 contains keys 29 and 30, integrators 31 and 32, differential amplifier 33, and storage device 34.

Amplifier 1 input is connected to an AM input signal source, and an output is connected to the first (signal) input of the synchronous demodulator 2 and through the driver 3 of the control voltage with its second (control) input and the first input of the measurement mode setpoint 12. The first output of the synchronous demodulator 2 is connected to the second input of the measurement mode setting unit 12 and through the rectifier 4 envelope and the normally open key 13 to the first input of the integrator 17 and the second output of the synchronous demodulator 2 via the normally open key 14 to the first input of the integrator 18. The output of the integrator 17 is connected to the first input of the comparator 6, through a normally closed key 8 to the first input of the comparator 7 and through a normally closed key

B

3797502

16 - with its second input, and the output of the integrator 18 - with the second inputs of comparators 5 and 6, via the normally closed key 9 - with its second input and through the normally open key 15 - with the third input of the integrator 17. Control inputs of the keys 13 and 14 connected to the Q second output of the unit 12 measurement mode and through the first inverter

19 to the first input element And 21, the second input through the second inverter

20 connected with an exit kompara-. Chapter 7. Control inputs of keys 9

and 16 are connected to the output of the element 21, the control input of the switch 15 to the output of the inverter 19.

Vkod. the comparator 7, the second inlet2Q house connected to the common busbar, is connected to the input of the indicator unit 11. The control input of the key 8 is connected to the output of the driver of 10 commands, the first and second inputs connected to the outputs of the comparators 5 and 6, respectively, and the third input to the output the inverter 19. The first input of the setting unit 12 of the measurement mode via the divider 22

30, the decoder 24 is connected to its first output, while the second input of the decoder 24 is connected to the output of the former 23 of the sampling period code. Second input setting device 12

35 of the measurement mode through the amplifier-limiter 26, the frequency divider 23 and the decoder 25 is connected to the eye with its output, while the second input of the decoder 25 is connected to the output of the measurement time code generator 28. The first (signal) input of the synchronous demodulator 2 via a normally open key 29 is connected to the first input of the integrator 31,

45 by the output connected to the input of the integrator 32, to the first input of the differential amplifier 33 and to the first output of the synchronous demodulator 2. The start of the integrator 32 is connected to

50 with the second input of the differential amplifier 33 and the second output of the demodulator 2.

The output of the differential amplifier 33 through a normally open

55 key 30 and memory 34 are connected to the second input of integrator 31, while the control inputs of keys 29 and 30 are connected to the second and third (control inputs of demodulator 2. The AM synchronous demodulator 2 is an interpolating filter that implements recovery of a continuous function (AM signal envelope) from its discrete samples. Unlike analog low-pass filters, interpolating filters that realize the recovery of a continuous function from its discrete samples provide high accuracy and speed at relatively low order of transfer function. When selecting a sampling frequency that exceeds the upper relative frequency of the envelope by 6 times, the level of high-frequency sampling noise does not exceed 1%. In this case, the transients end in two sampling periods.

The Converter operates as follows.

The input of the amplifier 1 receives the AM signal of the form (Fig.2.1)

V (t) V (1 + msinUt), (1) VG

where V is the amplitude of the unmodulated

load bearing; and - angular frequency of the carrier,

u) 2iTf; SI is the angular frequency of the envelope,

 I 2 F;

m is the modulation coefficient. The voltage (t) is fed to the signal input of the demodulator 2 and the input of the imaging unit 3, K, is the transfer coefficient of the amplifier 1. The output of the imaging unit 3 produces rectangular frequency pulses w with fronts corresponding to the zero-crossing voltage of the carrier frequency (Fig 2.2), arriving at the second (control) input of demodulator 2 and to the input of frequency divider 22, setting 12. As a result of a one-to-one comparison of the output signal of frequency divider 22 with the generator code 27, at the output of the decoder 24, rectangular pulses ( u. 2.3) with a period of K

T

where Kj is the division factor

driven by shaper. Rectangular frequency pulses oJ from the output of shaper 3 are received

to the control input of the key 29 of demodulator 2, opening it at time intervals corresponding, for example, to the positive half-waves of the input AM signal. Low-pass filtering of the signal formed at the output of switch 29, and extracting from it the frequency envelope SI, consist in its double integration by integrators 31 and 32 at each sampling period Tn and the feedback voltage from the output of differential amplifier 33 through Key 30 and a memory device 34 to the second input of the integrator 31. As a result, the output of the integrator 32 forms a voltage containing the envelope of the input AM signal and a constant component proportional to the level of the carrier (Fig. 2.4)

V, (t) K, K (mV sin P t + V), (3)

where K. is the path transfer coefficient: key input 29 is the integrator output 32. Simultaneously from the low frequency

filtering at the integrator output

31 the first derivative is formed

signal (3), i.e. (Fig. 2.5)

V (t) K, K, K mVcos L t.

(four)

Q 45 - CQ

35

55

where K is the path transfer coefficient: key input 29 is the integrator output 31.

The voltage (4) is detected by the rectifier 4 (Fig. 2.6) and / through the limiting amplifier 26 and the frequency divider 23 arrives at the first input of the decoder 25. As a result, one can compare the output signal of the frequency divider 23 with the driver code 28 at the output of the decoder 25 rectangular pulses are formed, the duration of which is a multiple of the envelope period of the AM signal (Fig. 2.7):

", Fri, (5)

where, 2,3, ...;

T - is the envelope period.

At time 1d (Fig. 2.8), corresponding to the positive edge of the pulse at the output of the decoder 25 (Fig. 2.7), the keys 9 and 16 are opened by the output voltage of the element 21 and 21 (Fig. 2.1) and at the same time the keys 13 and 14 close. The outputs of the integrators 17 and 18 by the time t, the disconnection of the keys 13 and 14 (Fig. 2.8) form a moderate average V, voltage.

respectively:

f

one

Vc,

i V, (t) K, K,

0

(6)

VCP

S V, (t) dt

iK, V, (7)

Where

2

the time constant of the integrator 17 on the first input; i} is the time constant of the integrator 17 at the input connected to the output of the key 13; Kf is the coefficient of the shape of the envelope. After unlocking the key 13 at the moment t, (Fig, 2.8), the integrator switches to the voltage storage mode — comparator 7, the Voltages (6) and (7) arrive at the first inputs of the comparators 6 and 5, where their values are compared with KjH and And, respectively, which determine the minimum allowable values of the envelope and carrier voltage 5 (K is the transfer coefficient of the comparator 6 at the second input).

Ppi and ev.r and I, p7

ment t,

5 from Wed on

(FIG. 2.8) the output voltage from the third output of the measurement mode setting unit 12, through the command shaper 10, opens the key 8, and the output voltage of the integrator 17 converts the comparator 7 into the unit state (FIG. 2.9). At the same time, the key 14 is opened and the key 15, connecting the output voltage (7) of the integrator 18 to the second input of the integrator 17, closes. The voltage (7) has an opposite field compared to the voltage lV.j (t) | and the output voltage of the integrator 17 will begin to decrease linearly in magnitude. At time t-j, the output voltage of the integrator 17 will become

equal to zero:

V,

All with And, And, p mi (6) and (7)

Vcp (4 - t,), (o, (8)

one

expressions are defined as appropriate.

Hence tCm) t - t, (, /,), m (9)

At time tj, the output voltage of the comparator 7 takes a zero (Fig. 2.9), and the output voltage of the And 21 element is a single (Fig. 2.10) value, which ensures the opening of the keys 9 and 16 that convert the integrators 18 and 17 to the original condition. Thus, the indicator unit 11 receives pulses (FIG. 2.9), the duration of which t (m) is proportional to the modulation factor of the input AM signal.

Further, the operation cycle is repeated. The transmission coefficient of the comparator 6 at the second input determines the insensitivity zone of the converter according to the modulation coefficient converted by the device, independent of the carrier level of the input signal,

Claims (1)

Invention Formula five 0 five 0 The modulator of the amplitude-modulated signal contains the input signal amplifier, the output connected to the first input of the synchronous demodulator and through the driver of the control voltage to the second input of the synchronous demodulator and to the first input of the settransmitter and the first By the code of the synchronous modulator connected to the third input, the first output connected to the second input of the measurement mode setting unit and the envelope rectifier input, the output of the envelope rectifier and the second the output of the synchronous demodulator is connected respectively to the first inputs of the first and second keys, the second inputs connected to the second input of the measurement mode setting unit, the outputs of the first and second keys are connected respectively to the first inputs of the first and second integrators, the output of the first integrator is connected to the first input of the first comparator and through the third key with the second input of the first integrator, and the output of the second integrator with the first input of the second comparator and through the fourth key with the second input of the second the integrator, the outputs of the first and second comparators are connected respectively to the first and second inputs of the first element I, the output connected to the first input of the fifth key, the second input of the second comparator is connected to the source of the reference voltage, the sixth key and the indicator unit, characterized in that , in order to simplify and improve noise immunity, the third comparator, the first and second inverters, the second element I are entered into it, the input of the first inverter is connected to the second output of the measuring mode setpoint, its output is temu input of the first AND gate and the first inputs of the sixth key and the second element And, the second input connected to the output of the second inverter, the output of the second element And connected to the second inputs of the third and fourth keys, the output of the fifth key to the first input of the third comparator, the second input connected to the common bus, the sixth output the key to the third input of the first integrator, the output of the third comparator to the inputs of the second inverter and the indicator unit, the second inputs of the fifth and sixth keys are connected respectively to the outputs of the first and second integrators, the second input ervogo comparator - to the output of the second integrator. Ppppppppppp t and pp p p p p p and and and t t it t and t t it t Fae 2