| 摘要 |
An improved VGA design offering a purely ratiometric mechanism for controlling gain by current-steering. A control loop delivers a reference voltage to a control amplifier that steers current and match the common mode output voltage (CMOV) with said predefined reference voltage. The VGA is designed so that, although the absolute gain varies over process, voltage, and temperature (PVT), the gain steps retain their values. Moreover, a method for controlling the gain in a VGA in a way that is insensitive to PVT is also disclosed. First, a voltage representing the required gain of the VGA in injected to the outputs of the VGA. Then, the CMOV of the VGA is sampled. Finally, the CMOV is subtracted by a predefined reference voltage and is fed back as bias to bases of the transistors of the VGA, thus controlling it gain, until the CMOV and the reference voltage become equal.
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