CMOS Wien bridge oscillator with switched capacitor resistors - has two amplifiers each producing 180 degree phase change and having unity and slightly above unity gain respectively

摘要

The oscillator includes two amplifiers (A1,A2). The output form the first amplifier (A1) is connected to its inverting input by a resistance (2RT) in parallel with a capacitor (CT). The output of the second amplifier (A2) is connected to its inverting input by two resistances (0.1 RA and 0.95 RA) mounted in series so that the source drain paths of two similar MOS transistors (M2,M2) are connected to the 0.1 RA resistor. The amplifier (A1) provides a phase shift of 180 degrees at a frequency determined by RC and a capacitor (CT), and has a gain of 1 between the input and the output. The amplifier (A2) is an inverter with a gain slightly greater than 1 (0.95 + 0.1) which allows oscillations to start. The frequency determining network can be implemented using switched capacitors which can be used to advantage in reducing floating node problems.