An orthogonal demodulator with auto gain control(AGC)function for wideband(0.8-2.7 GHz)receivers is proposed to realize the compatibility of receivers to multi-mode wireless communication standards and the AGC in the signal path. The demodulator adopts a wideband RF variable gain amplifier and an IF variable gain amplifier in the main signal path
while the frequency translation is performed by using a variable gain Gilbert cell. A root-mean-square(RMS)power detector is designed in the feedback path to detect the amplitude of output signal and then transfer it to a dc voltage. An AGC close loop system is formed through controlling the gain of blocks in the main path by the output voltage of the power detector. The demodulator just adopts analog circuits to realize AGC function
and avoids the drawbacks of traditional digital-assisted AGC mechanism
such as much more pins
complex algorithms and limited resolution resulted from a finite step length. The demodulator is implemented with 0.18 μm BiCMOS technology. Measurement results show that when the operation frequency is within 0.8 GHz to 2.7 GHz
the tunable conversion gain range of the demodulator is from -36 dB to 36 dB
and the demodulation bandwidth is 100 MHz; When the gain is in maximum
the noise figure is 9 dB
the error of the orthogonal phase is 1.6 degree and the error of the amplitude is 0.9 dB.
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references
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