A gain controlled amplifier circuit in which the amplifying element, such as a transistor, has its emitter-collector circuit connected to a gain control circuit which supplies a constant operating current and changes its AC impedance in accordance with an AGC signal. The gain control circuit includes a first branch having an impedance which varies with the externally applied AGC signal and a second branch having an impedance which varies with the current flow therethrough and which is connected to ground through an AC bypass. These two branches are connected in parallel to a constant current source so that the impedance of the first branch controls the current flow in the second branch and thereby its impedance.
A circuit in which signal gain is controlled independently of the quiescent direct current level. The quiescent current flows through a transistor connected as part of a constant current circuit and is modulated by signals applied to the base. The constant current circuit is connected in series with a pair of differentially connected transistors, both of which are connected in series with the load. The percentage of the total direct current through the differentially connected transistors is controlled by a direct signal applied to one of them. A current through that transistor also flows to the constant current circuit through a diode, the impedance of which is controlled by the magnitude of the direct current through it. The diode, the constant current circuit and a capacitor are connected in a second loop, and part of the signal circuit flows through this loop in a magnitude determined by the impedance of the direct current biased diode. The remainder of the signal current and all of the quiescent direct current flow through the load. Thus, the amplitude of signal voltage across the load is controlled by the percentage of direct current that biases the diode. The capacitor may be eliminated by duplicating the remainder of the circuit and connecting the duplicate parts as a differential and amplifier system.
A video amplifier is disclosed wherein the luminance signal is applied to the collector circuit of a differential amplifier comprising two transistors, the color difference signal is applied to the base of one of the two transistors, and the primary color signal is derived across a load resistor coupled to the collector circuit.
A common-emitter amplifier having its dynamic voltage gain controlled by using a controlled emitter-follower to shunt the emitter impedance of the common emitter amplifier.
A color television receiver includes conventional circuitry for processing and detecting a received color television signal. Three chrominance-luminance matrices combine detected color difference and luminance signals forming color red, blue and green video signals. Emitter follower coupling stages apply the color video signals individually to each of three output amplifiers which in turn drive the cathode electrodes of a unitized gun CRT. Potentiometers couple the emitter electrodes of the output amplifiers to a source of operating potential providing a simultaneous signal gain and DC output voltage adjustment for each amplifier during CRT color temperature setup. A voltage divider controls the voltage applied to the common screen grid electrode of the CRT providing a master setup adjustment.
A signal composing circuit suitable for a decoder device of a 4-channel matrix stereophonic system comprises two types of circuit units, one being a differential type circuit in which the common emitters are connected to ground through constant current means, the other having a like circuit arrangement as the differential type circuit but having constant current means shunted with a capacitor so as to ground the common emitters for A.C. signals. The signal composing circuit is suited for monolithic integrated circuits.
