This letter presents a simple approach for ultra-low-power and high-frequency variable gain amplifier (VGA) design, which requires no additional circuitry to generate the exponential-like function. Thus, the power consumption and chip area of the designed VGA can be drastically reduced without deterioration of other performance. The inverse exponential-like dB-linear characteristic is achieved by utilizing a pair of complementary transistors as the load. The p-MOS transistor is self-biased in the saturation region, while the n-MOS transistor is biased in the sub-threshold region. To prove the concept, a five-cell VGA is fabricated in a standard 0.18 μm CMOS technology. The measurements show that the power consumption of the VGA is less than 150 μW and achieves a total gain range of 71 dB, out of which 45 dB is dB-linear with less than 1 dB gain error, as well as bandwidth of more than 50 MHz. The output P1 dB is better than 0 dBm and the minimum input-referred noise is 7.5 nV/√Hz.
- CMOS variable-gain amplifier
- ultra-low power