JPS62118614A - Am modulation circuit - Google Patents

Abstract

PURPOSE:To stabilize the carrier level and modulation by adjusting the gain of a modulated wave amplifier circuit in response to an output of the 1st comparator so as to bring the polarity of the output of the 1st and 2nd comparators in a direction stabilizing respectively the level modulation of a carrier component in an output of the modulated wave amplifier circuit with respect to a modulated wave. CONSTITUTION:An output 113a of a carrier level setting device 13 and a DC voltage 106 of an output of the 1st filter 6 are compared by the 1st comparator 14, its output adjusts the gain of a modulated wave amplifier circuit 3 as an error voltage 114 to make a carrier output level constant. Further, a carrier level setting device 13 outputs a DC voltage 113b and a modulation level setting device 11 outputs a DC voltage 111 set to obtain a required modulation in response to the DC voltage 113b. The 2nd comparator 12 compares the DC voltage 111 with a DC voltage 108 being the output of a rectifier 8 and applies the difference voltage to a variable attenuator 10 as an error voltage 112. The adjusted modulation wave 110 is fed to an AM modulator 2, which is operated to be a required modulation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an AM modulation circuit suitable for high modulation frequencies.

(Prior Art) Generally, an AM modulation circuit employs a negative feedback detection method to improve modulation distortion and modulation degree stability.

(Problems to be Solved by the Invention) However, in the conventional AM modulation circuit, when the modulation frequency is high, there is no negative feedback amount, or even if there is, there is only a small amount of negative feedback, and there is a problem in the stability of the modulation degree.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an AM modulation circuit with excellent modulation degree stability.

(Means for Solving the Problems) In order to solve the above-mentioned problems, an AM modulation circuit provided by the present invention includes an AM modulator that performs AM modulation on the output of a carrier wave oscillator using a modulated wave, and a a modulated wave amplification circuit with a variable gain that amplifies the output modulated wave; an AM detector that performs AM detection on the output modulated wave of the modulated wave amplification circuit; a first P wave device that removes wave components; an IT comparator that outputs a voltage that is the difference between a DC voltage representing a preset carrier wave level and the output of the tf1 wave device; a second f-wave device for extracting the modulated wave component; a rectifier for rectifying the modulated wave component of the output of the second r-wave device; and a modulation level setting for setting a DC voltage corresponding to a predetermined degree of modulation at the carrier wave level. a second comparator that outputs a voltage difference between the DC voltage equivalent to the modulation degree and the output of the rectifier, and a variable attenuator that adjusts the level of the modulated wave using the output of the second comparator. , the modulated wave amplification circuit adjusts the gain according to the output of the first comparator, and the polarity of the outputs of the first and second comparators is determined according to the modulated wave of the output of the modulated wave amplification circuit. It is characterized by a direction in which the degree of level modulation of each carrier wave component is stabilized.

(Example) Next, one embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

AM modulator 2 generates a carrier wave 101 output from carrier wave oscillator l.
is subjected to AM modulation using a modulated wave 110, and a modulated wave 102 is output. The output 109 of the modulated wave generator 9 is level-adjusted by the variable attenuator 10 and becomes a modulated wave 110. The variable gain modulated wave amplifier 3 amplifies the modulated wave 102 to a required carrier wave output level and outputs the modulated wave 103. The gain of the modulated wave amplifier 3 is set to the output 11 of the first comparator 14 so that the carrier wave output is constant against changes in ambient conditions.
4 will be automatically adjusted. The output 10 of this modulated wave amplifier 3
3 is outputted to the output terminal through the coupler 4. The combiner 4 extracts a part of the output, and this output to
4b is subjected to AM detection by the AM detector 5. One of the outputs 105 of this AM detector 5 is supplied to the 1f1 wave detector 6.

The first P-wave device 6 removes the modulated wave from the output 105, takes out a DC voltage 106 corresponding to the carrier wave level, and applies it to the comparator 14. The carrier wave level setter 13 is a reference DC voltage generation source of the carrier wave level, and the output IL3a and the DC' voltage 106 output from the first P wave device 6 are compared in the first comparator 14, and this output is used as an error voltage. As 114, the gain of the modulated wave amplification circuit 3 is set to AI, and it operates to keep the carrier wave output level constant. Therefore, the carrier wave output level is set by the carrier wave level setter 13 to the DC voltage IL3a.
The required level can be set by adjusting.

The output 105 of the AM detector 5 is also added to the second P wave S7. This P-wave device 7 extracts only the modulated wave component 107. The rectifier 8 rectifies the modulated wave component 107, extracts a DC voltage lO8 proportional to the degree of modulation, and applies it to the second comparator 12.

The carrier wave level setter 13 outputs a DC voltage 113b having the same magnitude as the DC voltage 113a, and this DC voltage 113
b is applied to the modulation level setter 11. The modulation level setter 11 outputs a DC voltage tit set so as to obtain a desired degree of modulation according to the DC voltage tt3b. The second comparator 12 compares the DC voltage 111 with the DC voltage 108 output from the rectifier 8, and applies the voltage of the difference between these DC heart pressures as an error voltage 112 to the variable attenuator IO. The variable attenuator 10 receives the output 109 of the modulated wave generator 9, adds attenuation according to the error voltage 112 to the output 109 to adjust the level, applies the adjusted modulated wave 110 to the AM modulator 2, and outputs the required signal. It operates to achieve the modulation degree. Furthermore, the dumbness of the first comparator 14 and the second comparator 12 is selected so that when the output 104a increases, the output t04a decreases.

(Effects of the Invention) As explained above, in the AM modulation circuit of the present invention, even when the modulation frequency is high, not only the carrier wave level but also the amplitude of the modulation wave, that is, the modulation degree, can be negatively fed back. The carrier wave level and modulation degree can be stabilized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. Agent: Patent Attorney Shinsuke Honjo Figure 1

Claims (1)

[Claims] An AM modulator that performs AM modulation on the output of a carrier wave oscillator using a modulated wave, a modulated wave amplification circuit with a variable gain that amplifies the modulated wave output from the AM modulator, and a modulated wave amplification circuit that amplifies the output of the modulated wave amplification circuit. An AM detector that detects AM waves and this AM
a first for removing the modulated wave component from the output of the detector;
a filter, a first comparator that outputs a voltage difference between a DC voltage representing a preset carrier wave level and the output of the first filter, and a component of the modulated wave of the output of the AM detector. a second filter that takes out the modulation wave component, a rectifier that rectifies the modulated wave component of the output of the second filter, and a modulation level setter that sets a DC voltage corresponding to a predetermined degree of modulation at the carrier level; A second comparator that outputs a voltage difference between the DC voltage corresponding to the modulation degree and the output of the rectifier, and a variable attenuator that adjusts the level of the modulated wave by the output of the second comparator, The modulated wave amplification circuit adjusts the gain according to the output of the first comparator, and the polarity of the outputs of the first and second comparators depends on the carrier wave component of the modulated wave output from the modulated wave amplification circuit. An AM modulation circuit characterized in that the direction is to stabilize the degree of level modulation.