| 摘要 |
In cases where a direct-current offset occurs in a differential signal output from a differential signal amplifier when a differential input signal is differentially amplified in a series of differential signal amplifiers, a direct-current offset component amplified is included in a differential signal output from a particular differential signal amplifier. To suppress the direct-current offset component, the differential signal is, at first, differentially amplified in a pair of transistors of a detecting amplifier, the direct-current offset component is extracted in a low-pass filter from the differential signal amplified, and compensating currents produced according to the direct-current offset component are input to a differential signal amplifier preceding to the particular differential signal amplifier to adjust the direct-current offset component of the differential signal to zero. Because the pair of transistors of the detecting amplifier inevitably have a high input impedance, the differential signal can be directly received in the detecting amplifier, so that the low-pass filter can be formed on a minimized layout area without considering its input impedance. Therefore, a multi-stage signal amplifying circuit can be manufactured on a small layout area while preventing a voltage level of the differential signal from exceeding an input dynamic range of the differential signal amplifiers.
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