A dB-Linear Programmable Gain Amplifier With Mixed-Signal Control for Wide-Gain Range and Low-Power Applications

A robust, cascaded unit cell-based programmable gain amplifier (PGA) with precise and accurate dB-linear characteristics using the exponential approximation of the MOS transistor is presented. The exponential function is precisely generated for the desired gain range by exploiting the sub-threshold characteristics of load transistors in the proposed unit-cell. The proposed PGA has dual-mode gain tunability using analog voltage control and 5-bit digital control. The proposed PGA achieves a gain range from
$-$
37 dB to
$+$
39 dB with wide bandwidth and very low power consumption. The proposed dB-linear PGA is designed and fabricated in a standard 40nm CMOS technology. The measurements demonstrate that the proposed PGA can achieve a wide dB-linear gain range of 76 dB for 32 digital gain settings and a gain error of less than
$\pm$
0.5 dB. At the maximum gain setting, the PGA exhibits a bandwidth of 1.1 MHz, input referred noise of 29.8 nV/
$\surd $
Hz, output P
$_{\mathbf{1dB}}$
of
$-$
4.7 dBm, and consumes only 167
$\mu$
W of power from a 1.1 V supply. The core area occupied by the PGA is only 0.003 mm
$^{\mathbf{2}}$
.