Abstract
In this paper, a large gain variable range, high linearity, low noise, low DC offset VGAs with a simple gain-dB variable circuit are introduced. In the VGAs chain, the last and the first VGAs employ Bipolar transistors, to improve the linearity and noise characteristics. And the middle three stages VGAs employ MOS transistors. The whole circuitry is designed in 0.35um BiCMOS process, including variable gain amplifiers (VGAs) , fixed gain amplifiers , gain control and DC offset cancellation parts. The automatic gain control loop (AGC) provides a process independent gain variable range of 60dB (including 50dB gain-dB-linearity variable range), with a 200us loop lock time, the VGAs provide a 73dB largest gain, the THD is less than 1% at a 1V(P-P) output level; the equivalent output integral noise is 0.011v/√hz@20MHz bandwidth. The whole area is 1173um*494 um, and the power is 7.1mA at 3.3V signal supply voltage.
Highlights
variable gain amplifiers (VGAs) are kinds of circuits that are very common in analog system
The VGAs are normally employed in a feedback loop to implement an automatic gain control amplifier
We design a DAC, so one can choose though the automatic gain control loop (AGC) or by the DAC to change the gain of the VGAs chain
Summary
VGAs are kinds of circuits that are very common in analog system They are widely used in CCD, disk[1][2][3], acoustics[4][5], detector[6][7] and communication systems[8][9][10]. Fig. gives a kind of applications of VGAs in communication systems All these systems which need VGAs have the same characteristic: the signal is weak and the signal power varies in a wide range. In CMOS technology, the gain-dB-linearity variable circuits cannot be realized directly. Several important characteristics are discussed; in the third part, the VGAs , AGC and the gain-dBlinearity variable circuits are referred; in the fourth part the layout and test results are given; in the final part, a conclusion is made
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