A high frequency apparatus includes an input terminal 21, a high frequency filter 22 to which a signal input into the input terminal 21 is supplied, a mixer 24, one input of which an output signal of the high frequency filter 22 is supplied to and an other input of which an output signal of a local oscillator 23 is supplied to, an intermediate frequency filter 25 to which an output signal of the mixer 24 is supplied, an output terminal 27 to which an output signal of the intermediate frequency filter 25 is supplied, and an electronic switch 30. The electronic switch is provided in the vicinity of the intermediate frequency filter 25, for making a passband characteristic of the intermediate frequency filter 25 substantially flat by closing both contacts, wherein opening and closing of the electronic switch 30 is controlled externally. Accordingly, the adjusting error of the high frequency filter can be reduced.
In a method for interference suppression using a quality-adjustable bandpass filter in a receiver circuit for carrier-modulated received signals (S.sub.IN), the bandpass filtered received signal (B.sub.out) is demodulated, and a switching process is triggered with the demodulated received signal (D.sub.out). In order to eliminate internal or self-induced interferences that would be caused by a switching process in the output portion of the receiver, a quality reduction of the bandpass filter is correlated with the switching process that causes the interference. The method is especially suitable in connection with circuits for infrared receivers, which can thereby be manufactured in a small size, without external components, and thus economically.
A heterodyne receiver includes a tuner to select a frequency of a received signal and a converter to change the frequency of the received signal to an intermediate frequency. A single-pole/double throw switch has an input coupled to an output of the converter, a first output connected to a first band-pass filter and a second output connected to an amplifier. A second band-pass filter is coupled to an output of the amplifier, and a demodulator is coupled to an output of the second band-pass filter to produce an output signal and a characteristics signal. A logic circuit is coupled to receive the characteristics signal and for by-passing the first band-pass filter if the characteristics signal is less than a predetermined threshold.
An adaptive band-pass filter for a wireless receiver comprises a band-pass filter associated with the receiver, the band-pass filter configured to selectively filter the received signal, and a switch responsive to a control signal, the switch configured to control the band-pass filter based on a level of the received signal.
A direct conversion tuner down-converts television signals, cable signals, or other signals directly from an RF frequency to an IF frequency and/or baseband, without an intermediate up-conversion step for image rejection. The direct conversion tuner includes a pre-select filter, an amplifier, an image reject mixer, and a poly-phase filter. The pre-select filter, amplifier, and the image reject mixer can be calibrated to provide sufficient image rejection to meet the NTSC requirements for TV signals. The entire direct conversion tuner can be fabricated on a single semiconductor substrate without requiring any off-chip components. The tuner configuration described herein is not limited to processing TV signals, and can be utilized to down-convert other RF signals to an IF frequency or baseband.
