A low-voltage CMOS exponential function circuit for AGC applications

This paper describes how to implement a CMOS exponential function circuit, which can be used for Automatic Gain Control (AGC) and Variable Gain Amplifiers (VGA). The proposed exponential function circuit is based on Taylor's series expansion, and it has been implemented using a V-I converter and a squarer circuit, both obtained from the same core cell. The first order term of Taylor's series is implemented by a constant bias current. The low-voltage (/spl les/3 V) low power CMOS core cell has an almost rail-to-rail differential-input swing. In the entire voltage control range, the dB-linear function achieves a 30 dB linear range. For a 20 dB range, the linearity error is less than /spl plusmn/0.5%.

[1]  Wouter A. Serdijn,et al.  Low-voltage low-power fully-integratable automatic gain controls , 1994 .

[2]  Ramesh Harjani,et al.  A low-power CMOS VGA for 50 Mb/s disk drive read channels , 1995 .

[3]  Mohammed Ismail,et al.  A simple low-voltage all MOS linear-dB AGC/multiplier circuit , 1999, ISCAS'99. Proceedings of the 1999 IEEE International Symposium on Circuits and Systems VLSI (Cat. No.99CH36349).

[4]  G.S. Sahota,et al.  High dynamic range variable-gain amplifier for CDMA wireless applications , 1997, 1997 IEEE International Solids-State Circuits Conference. Digest of Technical Papers.

[5]  A. Wyszynski,et al.  High-precision, programmable 1-10 MHz bandwidth, 0-20 dB gain communication channel for digital video applications , 1996, Proceedings of Custom Integrated Circuits Conference.

[6]  Mohammed Ismail,et al.  CMOS exponential current-to-voltage converter , 1997 .

[7]  Wouter A. Serdijn,et al.  Low-voltage low-power fully-integratable automatic gain controls , 1994, Proceedings of IEEE International Symposium on Circuits and Systems - ISCAS '94.

[8]  A. Abidi,et al.  A 50 dB variable gain amplifier using parasitic bipolar transistors in CMOS , 1989 .

[9]  Chorng-Kuang Wang,et al.  A BiCMOS automatic gain control amplifier for SONET OC-3 , 1995, Proceedings of the IEEE 1995 Custom Integrated Circuits Conference.