JPH0141219Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a digital AM demodulation circuit, and more particularly to a circuit that can demodulate an AM signal at high speed.

Prior Art FIG. 2 shows a circuit diagram of an example of a conventional AM demodulation circuit. In the same figure, the amplitude modulated video signal inputted to terminals 1a and 1b is rectified by a diode 2, the carrier component is removed by a low-pass filter 3, and the demodulated signal is sent to terminals 4a and 1b as an envelope-detected demodulated signal.
4b.

Problems to be Solved by the Invention Since the conventional circuit described above uses the low-pass filter 3, there is a problem that it cannot be used as a demodulation circuit for high-speed AGC. On the other hand, when processing a digitized amplitude modulated video signal, a digitally processable rectifier and a digitally processable low-pass filter are used, but since the low-pass filter is also used in this case, a demodulation circuit for high-speed AGC is used. There was a problem that made it unusable.

An object of the present invention is to provide a digital AM demodulation circuit that can demodulate AM signals at high speed without using a low-pass filter or the like.

Means for solving the problem In Fig. 1, the 90° phase shifter 6 is a phase shifting means for shifting the phase of the input AM signal by 90°, and the divider 7 is a 90° phase shifter 6.
The first one performs division of the output signal of and the input AM signal.
The inverse trigonometric function calculator ⁸ is an inverse trigonometric function calculator means for performing an inverse trigonometric function operation on the output signal of the divider 7, and the sin trigonometric function operator 9 is tan ^-1 .
The trigonometric function calculator means for performing trigonometric function calculations on the output signal of the inverse trigonometric function calculator 8, and the divider 10 are sin,
This is an embodiment of a division means for dividing the output signal of the trigonometric function calculator 9 and the input AM signal.

Operation The 90° phase shifter 6 shifts the phase of the input AM signal by 90°, and the divider 7 divides the output signal of the phase shifter 6 and the input AM signal.
The tan ^-1 inverse trigonometric function operator 8 performs inverse trigonometric function operation on the output signal of the divider 7, and the sin trigonometric function operator 9 calculates the output of the inverse trigonometric function operator 8. A trigonometric function operation is performed on the signal, and a divider 10 divides the output signal of the sin trigonometric function operator 9 and the input AM signal.

Embodiment FIG. 1 shows a block diagram of an embodiment of the circuit of the present invention. The amplitude of the carrier wave is A, the amplitude modulation degree is ma,
Suppose that an AM signal such as a=A{1+maV(t)}sin(2πct) enters the terminal 5, where the modulation signal V(t) and the frequency of the carrier wave are c. signal a
is a digital AM sampled at a constant sampling period.
It's a signal. The signal a is phase-shifted by 90 degrees by the 90 degrees phase shifter 6, resulting in a signal b as follows: b=A{1+maV(t)}cos'(2πct). When a/b is performed in the divider 7, a signal c is obtained as follows: c=tan(2πct).

The signal c is calculated by tan ^-1 in the tan ^-1 inverse trigonometric function calculator 8 to become a signal d with d = 2πct, and the sin trigonometric function calculator 9 calculates sin
is calculated and the signal e becomes e=sin(2πct). When a/e is performed by the divider 10, the signal is outputted from the terminal 11 as follows: =A{1+maV(t)} (1).

Here, since A is the amplitude of the carrier wave, it is constant, so if A is set to 1, equation (1) can be rewritten as =1+maV(t) (2). Since 1 in equation (2) is the DC component, in the end, terminal 11 receives the AM signal superimposed with the DC component.
This means that the component, ie, the envelope of the input AM signal, has been extracted.

Note that when the division in the divider 7 is b/a, the same result can be obtained if the arithmetic unit 8 is a cot ^-1 inverse trigonometric function arithmetic unit.

Further, similar results can be obtained by using a -tan ^-1 inverse trigonometric function arithmetic unit as the arithmetic unit 8 and a -sin trigonometric function arithmetic unit as the arithmetic unit 9.

Furthermore, when the sign of either one of the arithmetic units 8, 9 is set to negative, the sign of the output is inverted from the above case.

Furthermore, when the divider 10 is configured to divide the signals e and b, a similar result can be obtained by using a cos trigonometric function unit as the arithmetic unit 9.

Also, a -90° phase shifter may be used instead of the 90° phase shifter 6, and as the 90° phase shifter, -90°, a Hilbert phase shifter may be used.
You can use a filter.

Also, if the input AM signal is sampled at a frequency four times the frequency of the carrier wave, a -90° phase shifter is used, and the input AM signal is delayed by one sampling period as a -90° phase shifter. A delay circuit may also be used.

Further, a function table based on a ROM may be used for each circuit such as the 90° phase shifter 6, dividers 7 and 10, tan ^-1 inverse trigonometric function operator 8, and sine trigonometric function operator 9.

Effects of the invention The circuit of the invention includes a phase shifter that shifts the phase of an input AM signal sampled at a constant sampling period by 90 degrees or -90 degrees, and a phase shifter that shifts the phase of the input AM signal sampled at a constant sampling period. a first divider that performs division, an inverse trigonometric function operator that performs an inverse trigonometric function operation on the output signal of the first divider, and a trigonometric function operation that performs a trigonometric function operation on the output signal of the inverse trigonometric function operator. and a second divider that divides the output signal of the trigonometric function unit and the input AM signal or the output signal of the phase shifter, so the AM component at each sample point can be obtained. It has features such as being able to perform demodulation processing at a higher speed than the conventional method using a low-pass filter, and having a simpler structure and easier integration into an IC than a conventional method using a low-pass filter.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram of an embodiment of the circuit of the present invention, and FIG. 2 is a circuit diagram of an example of a conventional circuit. 5...AM signal input terminal, 6...90° phase shifter,
7, 10...Divider, 8...tan ^-1 inverse trigonometric function operator, 9...sin trigonometric function operator, 11...output terminal.

Claims (1)

[Claims for Utility Model Registration] (1) A phase shifter that shifts the phase of an input AM signal sampled at a constant sampling period by 90° or -90°, and an output signal of the phase shifter that a first divider that performs division with the input AM signal; an inverse trigonometric function operator that performs an inverse trigonometric function operation on the output signal of the first divider; and an inverse trigonometric function operator that performs an inverse trigonometric function operation on the output signal of the inverse trigonometric function operator. A digital AM demodulation circuit comprising a trigonometric function calculator that performs calculations, and a second divider that divides the output signal of the trigonometric function calculator and the input AM signal or the output signal of the phase shifter. (2) The phase shifter, the first and second dividers, the inverse trigonometric function arithmetic unit, and the trigonometric function arithmetic unit use a ROM-based function table. Digital AM demodulation circuit.