Switching the gain of the front end of a receiver to make best use of the dynamic range of an ADC

摘要

A variable gain digitization chain 102 suitable for use in a mobile phone having at least two possible gains in order to make the best possible use of the dynamic range of a, preferably 12-bit, analog-digital converter 103. This gain is switched as a function of the level of the signal received. In a preferred form the chain has high gain when the signal level is low and low gain when the level of the signal is high. The level of the signal is preferably by a circuit 114 that takes the average of the positive half waves of the received signal. Then, this average is compared with a threshold. If the average is below the threshold, the gain is switched over to its highest value. If not, the gain is switched over to its lowest value. The measurement and the switching are done at a time when the signal is present but is not carrying any information. The level of the signal is in any case measured by an analogue circuit, which may be an envelope detector 115, which controls the gain switching. The signal being digitised is first demodulated.