Abstract: An IF input signal corresponding to a selected reception channel is applied through an SAW filter to an IF-AGC circuit, the amplitude of the signal is adjusted to a prescribed level, and the signal is thereafter supplied to a down converter unit. The down converter unit selectively outputs a Low-IF signal provided by down-converting the IF input signal and the High-IF signal amplified without frequency conversion, in accordance with an external instruction. A filter circuit has its cut off frequency selectively set to pass the Low-IF signal only, or both the Low-IF and High-IF signals.

Abstract: An IF signal output from an IF amplifying circuit included in a tuner is converted to have a band width for transmission by an SAW filter and has unnecessary signals removed therefrom. Thereafter, the resulting signal has its gain made constant by an IFAGC circuit, amplified by an IF amplifying circuit, unnecessary band components are removed by a lowpass filter, and balanced IF signals are output from unbalance/balance converting circuit and provided to a QAM demodulating circuit.

Abstract: A received signal passed through an HPF is supplied to an input switching circuit where the signal is switched to any of HIGH BAND, MID BAND and LOW BAND circuitry. The received signal of each band circuitry is band-switched by an RF amplification input BPF, RF-amplified by an RF amplifier and then a resultant received signal is supplied from an RF amplification output BPF. The received signal is mixed with a local oscillation signal from a local oscillator circuit by a mixer circuit to generate an intermediate-frequency signal. The intermediate-frequency signal is supplied to a first IF amplifier circuit, a SAW filter and a second IF amplifier circuit. A PLL channel select circuit outputs a switching voltage for each band and conduct PLL control for the local oscillator circuit.

Abstract: Received digital CATV signals are branched by a directional coupler into signals flowing in a through direction and signals flowing in a branch direction. The signals output from the directional coupler in the through direction are then fed through an extraction circuit, a variable attenuator, and a wide-band amplifier so as to have a desired frequency range and a desired level, and are then fed to a distributor so as to be distributed, for output, into downstream signals to be fed to a downstream tuner and CATV signals to be fed to an analog/digital tuner. The signals output from the directional coupler in the branch direction are fed through a band-pass filter and a wide-band amplifier to a distributor so as to be distributed, for output, into VHF signals and FM signals. Upstream signals are fed through an extraction circuit to a terminal at which the CATV signals are received.

Abstract: A tuner has a receiving unit receiving a signal input from a CATV station to an HPF. In the receiving unit, the signal is attenuated by a PIN attenuator circuit with the gain based on the signal level, thereafter the signal is amplified over a broad frequency range by a buffer amplifier, the high frequency component is amplified by a high frequency amplifier, and converted to a desired intermediate frequency signal by a frequency converting circuit including an oscillating circuit and a mixing circuit. Thereafter, the signal is IF-amplified by an IF amplifier and output through a terminal. As the signal input to the amplifier succeeding the PIN attenuator circuit is prevented from attaining a high level, signal distortion at the time of amplification can be improved, and supply current to the amplifier can be reduced.

Abstract: In the digital CATV tuner, gain of a reception signal of a plurality of frequency bands is controlled by a PIN AGC circuit, a reception signal for each of the frequency bands selected from the reception signal is high-frequency amplified by a high-frequency amplifier circuits, a local oscillation signal corresponding to the frequency band to be received from the plurality of the local oscillation signal from local oscillation circuits and the high-frequency amplified reception signal for each of the frequency band are mixed by a mixer to output an intermediate frequency signal, and a digital signal component is obtained from the intermediate frequency signal. Therefore, various characteristics can be improved.

Abstract: A PIN attenuator circuit within a digital STB tuner is connected to an output-side of a high-pass filter, and a PIN attenuator circuit is connected to an input-side of high-frequency amplification input tuning circuits. A buffer amplifier is connected between the PIN attenuator circuits. The PIN attenuator circuits and high-frequency AGC circuits are controlled in common.

Abstract: An HPF for blocking an upstream signal and passing a downstream signal, an LPF for blocking the downstream signal and passing only an upstream data signal, a directional coupler for branching, and a high frequency relay for forming a through line are built in a shielded package integrally as a high frequency module, so as to restrain noise produced by a digital circuit from interfering. This enables the analogue circuit of the high frequency module and the other digital circuits to be built integrally in a network interface module mounted in a cable television set-top box. In addition, a single tuner is used for both analogue and digital signals. In doing so, the switching of an AGC voltage is problematic, which is done by an AGC switching circuit. With a network interface module mounted in a cable television set-top box, the circuit arrangement can be hence simplified, and improvements can be made on cost, size and power consumption.

Abstract: A data signal to a CATV station and a down signal from the CATV station are branched by a duplexer, the data signal is output to a duplexer through a return pass amplifying circuit while the down signal branched by duplexer is converted to a first intermediate frequency signal by an up converter IC, and further converted to a second intermediate frequency signal by a down converter IC and output.

Abstract: An IF signal output from an IF amplifying circuit included in a tuner is converted to have a band width for transmission by an SAW filter and has unnecessary signals removed therefrom. Thereafter, the resulting signal has its gain made constant by an IFAGC circuit, amplified by an IF amplifying circuit, unnecessary band components are removed by a lowpass filter, and balanced IF signals are output from unbalance/balance converting circuit and provided to a QAM demodulating circuit.

Abstract: A received signal passed through an HPF is supplied to an input switching circuit where the signal is switched to any of HIGH BAND, MID BAND and LOW BAND circuitry. The received signal of each band circuitry is band-switched by an RF amplification input BPF, RF-amplified by an RF amplifier and then a resultant received signal is supplied from an RF amplification output BPF. The received signal is mixed with a local oscillation signal from a local oscillator circuit by a mixer circuit to generate an intermediate-frequency signal. The intermediate-frequency signal is supplied to an IF amplifier circuit, a SAW filter and an IF amplifier circuit. A PLL channel select circuit outputs a switching voltage for each band and conduct PLL control for the local oscillator circuit.

Abstract: The tuner structure of the present invention includes: a circuit board on which electronic circuit components such as transistors and resistors have been mounted; a chassis angle; and a shield cover. In the tuner structure, a feedthrough capacitor for inputting/outputting a power, a control signal and the like is mounted to a metal plate disposed in parallel to the circuit board.

Abstract: The tuner structure of the present invention includes: a circuit board on which electronic circuit components such as transistors and resistors have been mounted; a chassis angle; and a shield cover. In the tuner structure, a feedthrough capacitor for inputting/outputting a power, a control signal and the like is mounted to a metal plate disposed in parallel to the circuit board.

Abstract: The tuner structure of the present invention includes: a circuit board on which electronic circuit components such as transistors and resistors have been mounted; a chassis angle; and a shield cover. In the tuner structure, a feedthrough capacitor for inputting/outputting a power, a control signal and the like is mounted to a metal plate disposed in parallel to the circuit board.

Abstract: An IF input signal corresponding to a selected reception channel is applied through an SAW filter to an IF-AGC circuit, the amplitude of the signal is adjusted to a prescribed level, and the signal is thereafter supplied to a down converter unit. The down converter unit selectively outputs a Low-IF signal provided by down-converting the IF input signal and the High-IF signal amplified without frequency conversion, in accordance with an external instruction. A filter circuit has its cut off frequency selectively set to pass the Low-IF signal only, or both the Low-IF and High-IF signals.

Abstract: Input CATV signals are received by a PIN diode where the signals are high frequency signals of a plurality of frequency bands including UHF band, VHF.cndot.HIGH band and VHF.cndot.LOW band, the respective selected high frequency signals are tuned to predetermined frequency by radio frequency input tuning circuit, amplified by radio frequency amplifying circuit, and tuned to a signal of a prescribed frequency by radio frequency output tuning circuit. The high frequency signal is converted to an intermediate frequency signal based on a local oscillation signal from a local oscillation circuit by means of a mixer circuit, and applied to an intermediate frequency amplifying circuit.

Abstract: A cable modem tuner includes, in the same casing, an up-stream circuit to transmit an up-stream data signal to a CATV station, and a reception circuit for receiving a down-stream signal via a HPF that removes the up-stream data signal. The reception circuit includes a select circuit that selects a signal of a desired frequency band out of one of three frequency bands, a signal processing block including three local oscillation circuits to convert a signal of a desired frequency band into an intermediate frequency signal of a desired channel using an oscillation signal of a corresponding oscillation circuit, and a down converter with a local oscillation circuit converting an applied signal into a signal for demodulating a received signal. The down converter provides a baseband signal used to demodulate a received signal by the QAM when a digital signal modulated by the QAM is received.

Abstract: A local oscillation circuit in a frequency converter circuit includes a resonant circuit, and a differential amplifier circuit connected to the resonant circuit. The differential amplifier circuit includes two transistors constituting a differential stage. One end of the resonant circuit is connected to the base of one transistor via a capacitive element, and to the collector of the other transistor via a capacitive element. The other end of the resonant circuit is connected to only the base of the other transistor via a capacitive element. Accordingly, an unbalanced oscillate operation is performed in the local oscillation circuit, leading to reduction of the phase noise caused by decrease in an oscillation output due to the trap phenomenon, and an improvement in reception quality.

Abstract: The tuner structure of the present invention includes: a circuit board on which electronic circuit components such as transistors and resistors have been mounted; a chassis angle; and a shield cover. In the tuner structure, a feedthrough capacitor for inputting/outputting a power, a control signal and the like is mounted to a metal plate disposed in parallel to the circuit board.

Abstract: There is provided a tuner capable of improving reliability thereof with reduced power consumption and reduced heat generation. In the tuner, one wideband amplifier circuit including one transistor constitutes a buffer amplifier. The wideband amplifier circuit is coupled with a first local oscillator circuit in a DC coupling style. With the above-mentioned arrangement, the buffer amplifier is allowed to have a simplified circuit construction and reduce noises. Since the amplifier circuit and the local oscillator circuit are coupled with each other in a DC coupling style, reduced power consumption can be achieved.