SYSTEM AND METHOD FOR FORWARD PATH GAIN CONTROL IN A DIGITAL PREDISTORTION LINEARIZED TRANSMITTER

摘要

A system and method for controlling the gain in the forward signal path (102) of a digital predistortion linearizer is disclosed. The loop gain of the predistortion system is driven to unity, where a separately controlled constant-gain observation path (104) allows accurate gain control of the forward path (102). This is divided into digital gain from the predistortion function and analog gain from a Voltage Variable Attenuator (WA) (130) in the transmitter. The invention balances the distribution between these two domains in order to maximize dynamic range and minimize noise in the forward signal path (102). In order to distribute the forward path gain accurately, the characteristic of the WA (130) must be well known. Since these devices tend to be non-linear, with variable characteristic over temperature and batch, the invention compensates for this non-linear behavior by tracking the varying transfer characteristic of the WA (130), giving a predictable local characteristic. Another aspect of the disclosed invention is the ability to operate with very low transmit power and loop gain levels, allowing accurate gain control during such scenarios as cell initialization, that require operation over a wide dynamic range.