Signal-Strength Detector Based on CMOS-Inverter Supply Current

Pseudo-logarithmic signal-strength indicators are usually realized using a chain of amplifiers with amplitude detectors at the output of each stage and summing the output of the amplitude detectors. It is shown that the same can be achieved by measuring the total supply current of a pseudo-differential self-biased CMOS inverter chain. CMOS inverters act as amplifiers, and their supply current indicates the input amplitude. Amplification and amplitude detection are combined in the same block. The supply current is measured by mirroring the current in the pass transistor of the regulator that is used to power the inverter chain. The noise floor is set by the initial stages of the chain. A 65-nm prototype has a 70-dB dynamic range with ±1-dB error. It occupies 0.08
$\text {mm}^{{2}}$
and consumes 1.2 mW from 1.5V. The input referred noise floor is 0.2-mV rms.