Abstract: In the field of telecommunications, there is frequently a need to deactivate two amplifier stages alternately. In order to do this, the amplifier stages are usually triggered in push-pull mode over separate control lines. Such control lines allow the undesired coupling-in of interference in the amplifier stages and in following circuit elements, particularly in high-frequency applications. The new amplifier arrangement enables two amplifier stages to be alternately deactivated and has a high degree of immunity to high-frequency interference. It is realized as an integrated circuit and has, alongside the two amplifier stages, a switching stage over which the one of the two amplifier stages can be low-resistance linked on the input end to a reference potential connection having reference potential and can be deactivated through this.

Abstract: An input circuit and a television tuner for at least two frequency bands. The television tuner has a joint pre-amplifier whose output is connected to two independent, switchable and tunable band-pass filter circuits for the two frequency bands, preferably extending from VHF band I up to and including the hyperband. To achieve a high selection effect with a simple circuit structure and low space requirement, a two-stage switching device is connected to the output of the pre-amplifier, to which device separate inputs of the independent band filters are connected. The input circuit has a pre-circuit filter comprising a frequency-determining capacitor, and a series circuit connected parallel thereto including three frequency-determining coils. The first coil, like the capacitor, is connected at one end to ground and the third coil, like the capacitor, has its output end connected to the pre-amplifier input.

Abstract: An input circuit comprises at least two input paths which are connected to a common input terminal and which are alternately connectable to a common output. The input paths form selection members for the UHF and VHF frequency range whose signals are amplified in a common preamplifier component. In order to avoid mutual influencing of the selection members with simple measures, the output of the VHF selection member is connected to the common output via an impedance of the UHF selection member and a switch is provided for connecting the impedance and the output of the VHF selection member to ground for high frequency. The switch is conductive during UHF operation and then short circuits the output of the connected VHF input path.