Fast, low-power receive signal strength indicator (rssi) circuit and method therefor

A receive signal strength indicator circuit, comprising:

• a plurality of serially-coupled amplifier stages each providing an amplified signal, wherein a first amplifier stage receives an input signal whose signal strength is to be measured, and a last amplifier stage provides an amplified output signal;
• a plurality of envelope detectors each comprising:
• an MOS transistor having a gate for receiving said amplified signal of a corresponding one of said plurality of serially-coupled amplifier stages, and a source for providing a receive signal strength indicator component;
• a current source having a first terminal coupled to said source of said MOS transistor, and a second terminal coupled to a second power supply voltage terminal;
• and
• a capacitor having a first terminal coupled to said source of said MOS transistor, and a second terminal coupled to said second power supply voltage terminal, and
• a selection circuit coupled to said source of said MOS transistor of said plurality of envelope detectors, wherein said selection circuit provides said receive signal strength indicator component of one of said plurality of envelope detectors having a desired liner range as a detected RSSI signal.

A method of measuring a receive signal strength indicator of a received signal, comprising:

• amplifying said received signal in successive ones of a plurality of amplifier stages;
• detecting corresponding envelope signals of outputs of said plurality of amplifier stages;
• determining which one of said corresponding envelope signals of said outputs of said plurality of amplifier stages provides a desired linear range;
• and
• providing an output RSSI signal in response to said determining.