A MEANS FOR DIGITAL GAIN CONTROL OF ANALOG SIGNALS
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2001-Oct-16
Digital or switched gain control of amplifier circuits is frequently required in the design of telephones and other audio products. Modifying the gain of an op amp circuit by digitally selecting various feedback resistors produces accurate gain values and simple gain control. In MOS integrated circuit (IC) technologies the MOS transistor can operate as an analog switch to perform this function. Unfortunately, bipolar IC technologies do not offer such a simple solution. When a bipolar transistor is used as an analog switch, an offset voltage exists between the collec- tor and emitter terminals and the switched base current flows in the signal path.