| 摘要 |
<p>A variable gain amplifier (20) uses a differential attenuator (22) to provide a floating, high-impedance differential input to which a differential input signal is applied. The differential attenuator is comprised of (N-1) attenuator stages, with each stage forming a pair of attenuator taps for providing an attenuated version of the differential input signal. Each pair of taps is coupled to the differential inputs of a respective gm stage. The differential outputs of the gm stages are coupled to the differential inputs of a high open-loop gain main amplifier (28). The transconductance of each gm stage is controlled by an interpolator (26) which provides a bias current to each of the gm stages in a sequential manner as a gain control voltage is swept from its minimum to its maximum values. A gain response is produced that is linear-in-dB relative to the gain control voltage.</p> |
