Television and data signals travel over coaxial cable. These signals are transmitted as radio frequency (RF) signals, and are approximately in the range of 50 MHZ to over 860 MHz. These RF signals are either analog or digital in nature, and tuner circuits are used for tuning into one of the channels within the RF signal. They typically require low distortion, low noise figure, low phase noise, 2nd and 3rd order filters. Filtering by the filters is required over the entire dynamic range of the approximately 10 dB RF input signal range. Desensitization of the filter, due to interference, also needs to be kept at a minimum. Ideally prior to filtering, a low noise figure front-end provides amplification of the RF signal prior to tuning. In U.S. Pat. No. 6,100,761 a low noise amplifier circuit is disclosed which can handle a wide frequency range as well as provide a wide amplification range.
Unfortunately, filters that provide 2nd and 3rd order filtering over this wide dynamic range suffer from a tradeoff between speed and power consumption. In order to handle broadband signals the tuner requires more power since a faster, more linear, circuit is required, where faster circuits consume more power and slower circuits consume less. Consequently, as the bandwidth for TV and data signals increases, the power consumption of the tuners increases. High linearity is needed for high bandwidth operation within the frequency band This increases heat dissipation and therefore is undesirable. It is also undesirable due to newer applications for tuners requiring lower power consumptions, such as telephone signal transmission via television cable networks.
It is therefore an object of this invention to provide a tuner circuit which offers a highly linear output signal having a low noise figure at low signal levels while advantageously keeping tuner power consumption to a minimum.