Modulators – Amplitude modulator – Nonlinear device controlled by modulating signal
Patent
1983-03-21
1985-05-28
Grimm, Siegfried H.
Modulators
Amplitude modulator
Nonlinear device controlled by modulating signal
331116R, 331117R, 331109, 332 38, 332 59, H03C 102
Patent
active
045203288
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
This invention relates to an amplitude modulation circuit (hereinafter referred to as an "AM circuit") and in particular to an AM circuit providing a constant degree of modulation.
Such an AM circuit providing a constant degree of modulation is built into a radio frequency (hereinafter referred to as "RF") modulator such as is used when a multiplexed sound signal being reproduced as by use of a video tape recorder (hereinafter referred to as "VTR") is supplied to an antenna terminal of a television receiver, for high frequency modulation of the VTR output, and is used to provide a modulation signal to be modulated (amplitude-modulated signal) using as a modulating signal a pilot signal of predetermined frequency necessary to discriminate the type of the multiplex sound signal.
DESCRIPTION OF THE PRIOR ART
A prior art AM circuit including its peripheral circuitry is shown in FIG. 1. The illustrated circuit consists of a modulating signal oscillator circuit 1, a carrier wave oscillator circuit 2 and a modulation circuit 3.
The modulating signal oscillator circuit 1 is comprised of resistors R.sub.1 ' through R.sub.6 ' and R.sub.11 ', transistors T.sub.1 ' and T.sub.2 ', capacitors C.sub.1 ' through C.sub.3 ' and C.sub.8 ' and a reed-filter 4, with its oscillator loop circuit being formed of the base of transistor T.sub.2 ', the collector of transistor T.sub.2 ', reed-filter 4, the base of transistor T.sub.1 ', the emitter of transistor T.sub.1 ', resistor R.sub.3 ', and with the loop being completed with the base of transistor T.sub.2 '. Modulating signal oscillator circuit 1 commences oscillation when the gain of this loop is 1 or more. The oscillator frequency is determined by the frequency selectivity of reed-filter 4 (for example, 922.5 Hz), and the wave form of the modulated signal is a sine wave f.sub.0 as shown in FIG. 2a.
The carrier wave oscillator circuit 2 is comprised of transistor T.sub.3 ', resistors R.sub.7 ' and R.sub.8 ', capacitors C.sub.4 ' through C.sub.6 ' and an inductance coil L.sub.1 '. The oscillator loop of the carrier wave oscillator circuit 2 is formed by the emitter of transistor T.sub.3 ', capacitor C.sub.6 ', and the collector of transistor T.sub.3 ', with the loop being closed by the emitter of transistor T.sub.3 '. Carrier wave oscillator circuit 2 commences oscillation when the gain of this loop is 1 or more. The oscillator frequency F.sub.0 is determined by the time constant of a resonant circuit 5 consisting of capacitor C.sub.6 ' and inductance coil L.sub.1 ', and is expressed in Equation 1: ##EQU1## The output wave form of carrier wave oscillator circuit 2 is shown in FIG. 2b, and appears as such because transistor T.sub.3 ' is caused to undergo a switching operation in accordance with the charging and discharging of capacitor C.sub.5 ' through resistor R.sub.8 '. However, in such a prior art circuit, it often occurs that high harmonic and side-band frequencies will tend to adversely affect the performance of the circuit shown in FIG. 1 (and other circuits not shown, i.e., a sound processing circuit) through a common grounded line and a power supply line.
Modulation circuit 3 is comprised of resistors R.sub.9 ' and R.sub.10 ', transistor T.sub.4 ', inductance coil L.sub.2 ' and capacitor C.sub.7 '. The carrier wave supplied from carrier wave oscillator circuit 2 to transistor T.sub.4 ' through resistor R.sub.9 ' is shaped by resonant circuit 6 composed of L.sub.2 ' and C.sub.7 ', which acts as a filter circuit to suppress the high harmonic and side-band frequencies generated in carrier wave oscillator circuit 2. The emitter potential of transistor T.sub.4 ' is varied by a modulating signal supplied to the emitter of transistor T.sub.4 ' from modulating signal oscillator circuit 1 through capacitor C.sub.2 ', and the current flowing through transistor T.sub.4 ' is thus modulated in accordance with this modulating signal. The gain of modulating circuit 3 is determined by the product of the impedance of resonance circuit 6, formed by inductance coil
REFERENCES:
patent: 3649929 (1972-03-01), Thompson
patent: 3870971 (1975-03-01), Takahashi et al.
patent: 3963996 (1976-06-01), Skerlos
patent: 4419634 (1983-12-01), Druegh et al.
Hosoya Nobukazu
Murakami Yoshihiro
Grimm Siegfried H.
Sanyo Electric Co,. Ltd.
LandOfFree
Amplitude modulation circuit having stable modulation characteri does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Amplitude modulation circuit having stable modulation characteri, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Amplitude modulation circuit having stable modulation characteri will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-871006