AM suppression with low AM-PM conversion with the aid of a variable-gain amplifier

Abstract

This paper proposes the use of a variable-gain amplifier instead of a hard limiter for amplitude modulation (AM) suppression with low AM-PM (phase modulation) conversion. A hard limiter shows phase shift variations through input-amplitude dependent changes in output waveform, combined with bandwidth limitations. It is shown that these can be kept small only for limiter bandwidths much larger than the input frequency. A linear amplifier with variable gain used for AM suppression does not suffer from this problem. A CMOS variable-gain amplifier with gain-insensitive phase shift has been designed for this purpose. The benefits and limitations of the technique are explored with reference to an experimental 2.5 pm BICMOS chip for a television IF demodulator. Experimental and simulation results indicate that the AM-PM conversion can be kept below 0.5" at 40 MHz over an input amplitude range of 20 dB, where typical hard limiters show 3-5". This is achieved with an amplifier bandwidth of 80 MHz, while a hard limiter would need a bandwidth of more than 600 MHz to obtain similar results.

Impact of AAC design on phase noise performance of VCOs

“…This noise is upconverted by the "mixer" action of the switching transconductor, and in principle its contribution should be only amplitude noise at the output of the synthesizer [13]. However the bias current noise contributed by the AAC does not produce only amplitude modulation [15], which may be otherwise rejected with a limiter on the output. It also affects the oscillation frequency, and thus the phase, through two distinct mechanisms.…”

“…The simplest technique to predict the mean autocorrelation area in all the cases, is to take the arithmetic average of and . Performing little approximations, a more compact rule of thumb for estimating the noise power density results in (15), shown at the bottom of the page. After term redefinition, (15) eventually becomes (8).…”

A High-Linearity Digital-to-Time Converter Technique: Constant-Slope Charging

“…Moreover, as CMOS interconnect losses are high and frequency dependent, different amplitudes and waveforms result at different delay tap-points along a transmission line, which introduces zero-crossing variations when sensed by a comparator [13]. Lumped circuits such as all-pass filters can approximate a true time delay compactly [14][15] and maintain signal waveform, but noise and dynamic range are compromised.…”

CMOS Limiting Amplifier and RSSI (Received Signal Strength Indicator)

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