AM Suppression with Small AM-PM Conversion by Means of Variable Gain

This paper proposes the use of a variable gain amplifier instead of a hard limiter for AM suppression with a low AM-PM conversion. Measurements and simulations indicate that the AM-PM conversion can be kept below 0.5° at 40MHz over a gain range of 20 dB in a 2.5μ BICMOS process, where typical hard limiters exhibit 3-5°. This is achieved at 80MHz bandwidth, while a hard limiter would need more than 600MHz bandwidth to obtain similar results.