| 摘要 |
In an operational amplifier (op amp) for use in an integrated circuit (IC) device, a first field effect transistor (FET) in a current-mirror circuit is connected, and provides a bias current, to at least a second FET in a differential amplifier. As the voltage of the power supply to the op amp decreases in response to the advance of IC technology, the first FET operates in a non-saturation region of its output characteristics. As a result, the current provided by the first FET to the differential amplifier varies substantially with a common-mode signal, whose signal level equals the average of those of non-inverting and inverting input signals to the differential amplifier. Consequently, the op amp imparts a significant gain, referred to as a common-mode gain, to the common-mode signal, which is undesirable. To reduce such a common-mode gain, in accordance with the invention, the bias current provided by the first FET is measured to adjust a second current which affects the output of the op amp.
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