| 摘要 |
PURPOSE: An operational amplifier comprising a common mode feedback circuit is provided, which occupies a small chip size and is appropriate for a high speed operation. CONSTITUTION: A folded cascode operational amplifier circuit comprises a folded cascode gain unit including a differential input section, a cascode current mirror and a cascode current source, and a common mode feedback circuit. The common mode feedback circuit comprises two capacitors, and is connected to both output ports of the folded cascode gain unit to seize a common mode of a differential output voltage to the folded cascode operational amplifier circuit. According to the common mode feedback circuit, the first switch transfers a bias voltage(BIAS4) to one end of the first capacitor, and the second switch connects a signal line(CML) to another end of the first capacitor. The third switch connects one end of the first capacitor to an output port(CMFB). The fourth switch connects another end of the first capacitor to a differential output port(OUTT). The fifth switch transfers the bias voltage to one end of the second capacitor, and the sixth switch connects the signal line to another end of the second capacitor. The seventh switch connects one end of the second capacitor to the output port(CMFB), and the eight switch connects another end of the second capacitor to the differential output port.
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