In the transmission of signals between a transmitter and a receiver, such as voice signals, it is necessary for the receiver to have a certain dynamic range in order for the signals to be correctly reproduced. Signal strengths can vary markedly when received by the receiver, and a wide dynamic range contributes towards better signal reproduction in the receiver. For instance, U.S. Pat. No. 5,276,685 teaches a method of adapting the strength of an incoming signal to the receiver to the ability of the receiver to receive the signal, so-called automatic gain control. When the strength of the signal received by the receiver is greater than an upper limit value of the dynamic range of the receiver, the signal is attenuated. When the strength of the signal received by the receiver is beneath a lower limit value of the dynamic range of the receiver, the signal is amplified. One drawback with the method taught by the U.S. patent resides in the requirement of such complicated equipment in addition to the equipment normally available in the receiver. This additional equipment adds to the cost. Problems also occur when the strength of the received signal varies very abruptly. U.S. Pat. No. 4,893,316 teaches another method of extending the dynamic range. The patent describes dithering. By dithering is meant briefly the application of known noise to a signal which is too weak to be detected. The signal superimposes the noise. The signal can be detected by amplifying the total signal and filtering-out the known noise. The drawback with dithering lies in the requirement of components as dither generators and de-generators, which also add to the cost. The dynamic range can also be extended by extending the number of quantizing levels and using a 13-bit A/D-converter instead of a 12-bit converter. An increase in the number of bits results in more quantizing levels, which enables an extended dynamic range to be reproduced correctly. However, A/D-converters that have such extended properties also add to the costs and may be difficult to achieve.
USPTO Backgrounds
USPTO Backgrounds