| 摘要 |
A direct conversion tuner for tuning either analog or digital television signals includes a first (A) and second (B) channels, each having first (MIA) and second (MIB) mixers and an intervening filter stage (LPF A and LPF B), coupled between an RF input and an output combining unit (SU1). The first mixers receive respective first local oscillator signals which have the same frequency (WO) but a quadrature phase relationship. The frequency of the first local oscillator signals is controlled according to the selected channel so that it is located within the spectrum ofthe respective RF signal. The second mixers receive respective second local oscillator signals which have the same frequency (WN) but a quadrature phase relationship. The frequency of the second local oscillator signal is located above the passband of the filter stages. A digital gain and phase equalization network (GC and PC) is included in one of the channels for adjusting the relative gain and phase shift of the two channels and is automatically controlled by a microcomputer (MC) in response to signals sampled at respective points (A and B) within the first and second channels to reduce the relative gain and phase shift. As a result, near perfect cancellation of unwanted components occurs in the output combining unit. |
