A variable gain element for adjusting a magnitude of an input signal. The variable gain element includes a first differential transistor pair having a first transistor coupled to a second transistor. A second differential transistor pair couples the second transistor to a supply voltage and to an output...http://www.google.com.hk/patents/US6452445?utm_source=gb-gplus-share專利 US6452445 - Voltage controlled variable gain element
