摘要:
A tuner for receiving signals broadcast on two spaced bands, each divided into several channels, has two fixed bandpass filters, one to pass all of the channels in the lower band between the lowest frequency f.sub.P of the lowest channel and the highest frequency f.sub.S of the highest channel of the lower band, and the other to pass all of the channels in the upper frequency band between the lowest frequency f.sub.T of the lowest channel and the highest frequency f.sub.W in the highest channel of the upper band. The bandwidth of each channel is f.sub.B. The tuner includes an amplifier and a third filter to which signals of either band are supplied by selective operation of a switch. The third filter has a cut-off frequency below the second harmonic of the lowest frequency of the upper band to simplify the avoidance of image interference from second harmonic signals of the band. A tunable local oscillator supplies a heterodyning signal to the mixer to convert any selected channel of the received signal to an intermediate frequency (i.f.) band, and image interference is avoided by setting the local oscillator frequency f.sub.n required to convert channel n to the i.f. at a frequency above that channel such that the lowest frequency f.sub.L of the i.f. band satisfies the following conditions: ##EQU1##
摘要:
A tuner for receiving signals broadcast on two spaced bands, each divided into several channels, has two fixed bandpass filters, one to pass all of the channels in the lower frequency band and the other to pass all of the channels in the higher frequency band. The tuner includes a mixer to which signals of either band are supplied by selective operation of a double-throw switch. A tunable local oscillator supplies a heterodyning signal to the mixer to convert any selected channel of the received signal to an intermediate frequency (i.f.) band chosen to avoid image interference from undesired channels, whether the local oscillator frequency is above or below the selected channel. To ease the constraints on the choice of the i.f. band, different i.f. filters tuned to first and second i.f. bands may be used for the higher and lower received bands. A second double-throw switch ganged with the first switch can then be used to direct the heterodyned signals to the proper i.f. filter.
摘要:
A high-frequency modulator circuit including a frequency multiplier comprised of a first differential amplifier for receiving a base oscillating signal and for multiplying the frequency of the base oscillating signal to thereby produce a higher frequency carrier signal; and a modulating circuit connected to the first differential amplifier for modulating the carrier signal with input information. The first differential amplifier includes a pair of output terminals; and the modulating circuit is comprised of a second and third differential amplifier, each having a pair of input terminals connected to the respective output terminals of the first differential amplifier such that the higher frequency carrier signal is applied differentially to each of the second and third differential amplifiers. The second and third differential amplifiers each includes a pair of output terminals, the second differential amplifier output terminals being connected to oppositely phased ones of the third differential amplifier output terminal. The input information is supplied to at least one of the second and third differential amplifiers to thereby vary the higher frequency carrier currents which flow therethrough.
摘要:
A signal to be controlled is applied to the base of an emitter-follower input transistor, the emitter of which is connected to an input terminal of a differential amplifier. This input terminal of the amplifier is connected by a diode to a controllable current source so that the base current of the differential amplifier input transistor is controlled. A constant current source is connected to the common emitter circuit of the differential amplifier, and the gain of the circuit is determined by the ratio of current in the latter source to current in the controllable source. A current conducting circuit, such as, an emitter load resistor, is connected to the emitter of the input transistor to hold the output impedance thereof at a substantially constant low value inspite of changes in the current of the controllable current source, Maximum gain of the circuit may be determined by separating the controllable current source into a controllable portion and a fixed portion in parallel so that the minimum current is at least as great as the current of the fixed portion. This limits the maximum circuit gain by limiting the maximum ratio of fixed current to controllable current. A fixed voltage source connected to the common circuit point between the controllable current source and the diode assures that the gain of the circuit will not fall below a selected minimum value.
摘要:
A television sound receiver having an input terminal for receiving a television sound signal, a tuner including a local oscillator connected to the input terminal, an intercarrier sound demodulating circuit connected to the tuner, a split-carrier sound demodulating circuit, including a limiter amplifier connected to the tuner, a sound signal output terminal, and a switching device for selectively and operatively connecting either the intercarrier or split-carrier sound demodulating circuits between the tuner and the sound signal output terminal. Additionally, the receiver includes an error detecting device connected to the split-carrier sound demodulating circuit for detecting the frequency error of the local oscillator and a first operational device which is responsive to an output signal from the error detecting device and which produces a first operational device output signal which activates the switching device such that the split-carrier sound demodulating circuit is operatively connected between the tuner and the sound output terminal when the output signal from the error detecting device is less than a predetermined level. Level detectors are connected to the limiter amplifier and detect a level of the split-carrier sound signal. A second operational device, which is responsive to the output signal from the level detectors, produces an output signal which activates the switching device such that the intercarrier sound demodulating circuit is operatively connected between the tuner and the sound output terminal when the output signals from the level detectors are less than a predetermined value.
摘要:
A muting circuit for a television or AM signal receiver which uses a synchronous detector.The muting circuit includes an input terminal for receiving an amplitude modulated signal, a synchronous detector for detecting such AM signal, a circuit for supplying a reference signal having a predetermined frequency and phase to the synchronous detector, an amplifier, a circuit path for delivering to the amplifier the detected signal produced by the synchronous detector, a level detecting device connected to the output of the synchronous detector for producing an excess signal when the detected signal exceeds a predetermined level, an integrator for producing a muting signal in response to the production over an extended period of time of the excess signal, and a switching device connected to the amplifier for muting the signal produced by the amplifier in response to the production of the muting signal.
摘要:
A television receiver has an automatic fine tuning circuit with a first phase-locked loop including a first low pass filter and a synchronous video detector with a second phase-locked loop including a second low pass filter. The cut off frequency of the first low pass filter is selected lower than the cut-off frequency of the second low pass filter, thereby enabling a stable operation of two phase-locked loops simultaneously.
摘要:
Demodulating apparatus for a modulated signal comprised of a carrier deriving circuit which is supplied with the modulated signal and which derives an unmodulated carrier therefrom, the carrier deriving circuit including a tuned circuit having a center frequency substantially coincident with the carrier frequency of the modulated signal and a limiter circuit in which the limiter circuit imparts a phase shift to the signal supplied thereto in connection with its elimination of the amplitude fluctuations in the signal produced by the tuned circuit. A synchronous detector receives the modulated signal and the derived carrier so as to detect the modulated signal with the derived carrier. A phase shift circuit supplies the synchronous detector with a phase shifted modulated signal, the phase shift substantially compensating for the phase shift imparted by the limited circuit in the carrier deriving circuit, whereby the modulated signal and the carrier which are applied to the synchronous detector are substantially in phase with each other.
摘要:
A transistor biasing circuit having a single biasing transistor for biasing first and second operational transistors. The biasing transistor has means connecting its base to its collector and means are provided to connect the base of each of the first and second operational transistors to the collector circuit of the biasing transistor. Each of the three transistors are arranged in a circuit between a pair of voltage terminals which are connected to a power supply. The arrangement of the resistors in the circuit paths of the biasing transistor and the operational transistors are in such a way as to provide circuit means for stabilizing the collector currents of the first and second transistors regardless of variations in the factor of h.sub.FE. This circuit arrangement provides an improved stabilization of the collector currents over prior art devices.
摘要:
A synchronous detector adapted to detect a modulated information signal, such as a video IF signal. The modulated information signal is provided in the form of a vestigial sideband signal. A band-pass filter including a tuned circuit tuned to the frequency of the carrier on which the information signal is modulated has a pass band which is less than the frequency spectrum of the vestigial sideband signal so as to limit the frequency spectrum of the signal passed by the filter to a double sideband signal. A limiter is coupled to the band-pass filter to receive the double sideband signal and for deriving a switching carrier therefrom, the frequency of the switching carrier being equal to the frequency of the carrier on which the information signal is modulated. An emitter-follower circuit is connected between the band-pass filter and the limiter so as to couple the double sideband signal from the filter to the limiter. A multiplier circuit has first input terminals coupled to the limiter for receiving the derived switching carrier and second input terminals for receiving the modulated information signal, whereby the modulated information signal is multiplied with the switching carrier to obtain the information signal.