Patent ID: 7613239
Filing Date: 2009-11-03
Classification: H03F,H04L

Abstract:
1. A digital signal offset adjusting apparatus comprising: an input terminal to which an input digital signal having a wideband frequency characteristic including a low frequency band, a direct current component, and a high frequency band is input; a direct current voltage generator which outputs a desired direct current bias voltage; an output terminal to output an output digital signal obtained by applying the direct current bias voltage output from the direct current voltage generator to the low frequency band, the direct current component, and the high frequency band of the input digital signal input to the input terminal; a capacitor which is connected between the input terminal and the output terminal and which causes the output terminal to pass through the high frequency band of the input digital signal input to the input terminal; a first coil, one end of which is connected to the input terminal, and which passes the low frequency band and the direct current component of the input digital signal to another end; a second coil, one end of which is connected to the output terminal; an operational amplifier, a first input end of which is connected to the other end of the first coil, a second input end of which is connected to the direct current voltage generator, an output end of which is connected to another end of the second coil, and which outputs to the output terminal via the other end of the second coil from the output end, the low frequency band of the input digital signal passed to the other end of the first coil input to the first and second input ends and a composite signal obtained by combining the direct current component and the direct current bias voltage output from the direct current voltage generator; and a frequency characteristic compensating circuit connected between a reference electrical potential point and the second input end of the operational amplifier or between the second input end and the output end, the compensating circuit being adopted to compensate for a frequency characteristic so that a gain of the operational amplifier increases with a component having a higher frequency from among the low frequency bands of the input digital signal passed to the other end of the first coil.