Electronically adjustable phase shifter using OTAs

Analog Multipliers-Based Double Output Voltage Phase Detector for Low-Frequency Demodulation of Frequency Modulated Signals

“…The used CMOS multiplier can be applied as a simple differential input differential output operational transconductance amplifier (OTA) [48]. We provided a survey (summarized in Table II) of solutions using OTAs applied (only OTAs are accepted as suitable active devices) in first-order all-pass filters (phase shifters) [49] and revealed the following conclusions: a) the zero/pole frequency cannot be adjusted simultaneously (as requested typically) by a single parameter in all cases (matching condition are required in each case except [50], [56]), b) solution [50], where the electronic adjustment is possible by single parameter, requires two floating capacitors (matched design) and does not possess highimpedance input (useful when exposition of the signal at input node to the frequency dependent load is an issue), c) linear voltage electronic tuning is not available in case of CMOS-based OTA solutions [51], [53], [54], [56], d) there are solutions without grounded capacitor unsuitable for on-chip integration [48], [50], [52], [54], e) available range of linear processing of signal levels in all-pass structures is not often reported or with quite low range, if tested [52], [56] (correct signal processing of our system requires operation in hundreds of mV) and f) some matching condition is required for correct operation of all solutions presented in Table II (including our case) but the adjustment of zero/pole frequency has no influence on matching condition in our case (filter features) that is fixed during the adjustment.…”

“…Other solutions in Table II expect simultaneous driving of two [48], [53]- [55] or more transconductances and matching condition fulfilment simultaneously [51], [52] for correct operation. Our design supposes single parameter linear zero/pole electronic frequency adjustment, high-input impedance, grounded capacitor and linear dependency of transconductance on driving parameter (DC voltage).…”