SU731576A1 - Width-modulated signal demodulator - Google Patents

Description

based on the NAND element with open collector, resistive divider 6, connecting the output of the key 5 with the bus thread. The output of the divider 6 is connected to the inverting input 7 of filter 1 and through the key 3c to the input 8 of the device and the input of the emulsion detector 2. A resistive divider 9 is connected between the power bus and the common bus, the output of which is connected to the non-inverting input 10 of filter 1, whose output 11 is output devices, and the resistive divider 6 is made on the resistors 12 and 13, the combined outputs of which are connected to the output of the switch 3, the other output of the resistor 13 to the thread bar, and the other output of the resistor 12 to the output of the switch 5.

The demodulator of the width-modulated signal works as follows.

If there is a convertible signal at the input 8 of the device, the pulse detector 2 intended to indicate the absence of an input signal does not participate in the operation of the demodulator. The output of the pulse detector 2 in this case is a high voltage level and the resistor 12 is disconnected from the common bus of the device. The key 3 together with the resistor 13 of the resistive divider 6 at the same time works as a normal key stage, which inverts the phase of the input signal. From the output 11 of the device, a demodulated signal is removed, the value of which is proportional to the difference of the factors acting on the inputs of the active low-pass filter 1.

The voltage level set by the resistive divider 9 on the non-inverting input 10 of the active filter 1 is chosen so that the effect on the input 7 of the filter 1 pulses with a relative duration of 6 0.5 at the output 11 of the demodulated signal sial device is zero. In this case, the device operates as a linear time demodulator, which performs proportional conversion of the time and field in a DC voltage in accordance with the expression U, EQK-EK (l + K),

where 6 is the duration

interval ();

T is the period of the spontaneous modulated sigal oscillations;

/ С-coefficient and transmission amplifier filter 1; / Sd is the transfer coefficient of the resistive divider 9 associated with the noninverting input of the active low frequency fnltra.

From the expression (1) it follows that with the values of 6 0.5 and d. D I-. / t / bbix o

 : BUT)

and that the magnitude of the demodulated signal does not depend on the voltage fluctuations of the power source + Е.

When the signal being transformed disappears, the pulse detector 2 signals this event by changing the high level of the output voltage to the low. In this case, the key 3 is disconnected from the equal-shoulder resistive divider 6, the resistor 12 is connected via the key 5 to the common bus of the device, and the input 7 of the low-pass filter 1 is applied to a voltage level, almost equal to E / 2, which corresponds to the value of the constant component -modulated oscillations U EQ NRI 0 0.5 ..

In this case, the voltage at the output of the device AND in accordance with the expression (1) is zero.

Thus, when the latitude modulated signal disappears and the filter input automatically applies a voltage level corresponding to the constant component of the pulse train with a relative length of 0.5.

Since both resistive dividers are connected in parallel to the same filament source, the magnitude of the demodulated signal does not depend on the voltage fluctuations, due to the fact that the amplitude of the converted signal and the reference voltage level set by the resistive divider 9 and is directly dependent .

The proposed device, when used in video paths for receiving signals with PWM modulation, will eliminate the dependence of the output signal on the instability of the power supply, as well as provide for the automatic recovery of the zero level in the demodulated signal, which significantly improves the accuracy and stability of the width-modulated signal conversion.

Claims (2)

1. A demodulator of a latitude-modulated signal, containing an active low-pass filter, whose input circuits include switching keys, characterized in that, in order to increase the accuracy and stability of the transformation of the input signal, an impulse detector, an inverter and two resistive dividers, the outputs of which are connected to the inputs of the low-pass filter, the first divider being connected between the common bus and the imitation bus, and the second between the power bus and the common bus via a nerve key, the control input of which with It is connected to the output of the pulse detector through an inverter, the input of which is connected to the control input of the second switch, through which the device input is connected to the output of the second resistive divider, and the input of the pulse detector is connected to the input of the device. Sources of information taken into account in the examination 1. USSR author's certificate number 440766, cl. N OZN 7/10, 10.04.72. 2. Smolov V. B. and others. Time-pulse computing devices. L., 1968, p. 7, fig. 3 (prototype). 0 + L1