Quasi-direct conversion radio receiver architecture for use in mobile telephone, heterodyning RF input to low IF before digitizing

摘要

The device uses two mixer channels with local oscillator signals in quadrature and at a frequency chosen to produce a low, rather than zero, IF such as 100 kHz. After low pass filtering and gain control, the resulting I and Q signals are digitized and conventionally down converted by a second LO at IF and signal processor (20) including a complex mixer. The receiver comprises a first analogue mixer (4) combining a received signal (V3) with the signal from a local oscillator (6') at a first conversion frequency. A second analogue mixer (5) combines the input signal with that from the local oscillator phase shifted by 90 degrees. Each mixer defines a channel which is destined to be the object of analogue-digital conversion (11,12). On the digital side the receiver also comprises a device for detecting possible phase and gain imbalances between the two channels (I,Q). The first conversion frequency corresponds to the central frequency of the received channel, increased by half the frequency band of the channel.