VariableDelay LowPass AllPass Filters and their Applications

Abstract

newline newline newline newlineContinuous time filters offer a certain amount of delay to an input signal. The delay of these filters can be varied by changing the filter s time constant. This work mainly focuses on delay tuning techniques for low pass filters (LPF) and all-pass filters (APF). In the case of variable delay LPF, the delay of the filter is altered by changing the effective impedance of the circuit us- ing the principle of the Miller effect. In the case of APF realized with active Gm-C architecture, programmable delays are obtained using constant C frequency scaling techniques. These tech- niques of delay tuning are used in various real-time applications such as in realizing wideband tunable delay lines for beamforming, expansion, or compression of continuous time pulses and voltage-controlled oscillators. newlineThe first application of tunable delay Low Pass Filter (LPF) is in realization of true time delay (TTD) architecture for wideband beamforming applications. A 15-stage True Time Delay (TTD) circuit with delay correction is implemented in TSMC-65 nm CMOS technology with supply voltage of 1.2 V. Post layout simulation results show that 15 cascaded stages of the TTD newlinewith the proposed delay correction technique has a maximum delay variation of ±5 ps across newline1 GHz bandwidth with a power/delay-range factor of 0.1 mW/ps. A 3-stage voltage controlled oscillator (VCO) with a proposed variable delay cell in current mode logic (CML) is discussed. The proposed VCO architecture is implemented in TSMC-180 nm and 65 nm technologies. Results show that VCO has a tuning range of 56.4% with phase noise ofand#8722;76 dBc/Hz at offset newlinefrequency of 1 MHz. The VCO dissipates power of 7.2 mW from 1.2 V supply with figure of newlinemerit of 181.69 dBc/Hz. The next application of variable delay LPF would be in the expansion and compression of continuous-time pulses. A 15-stage expansion circuit is implemented in TSMC-65 nm CMOS technology respectively. A stretch factor of 2.2 is obtained for a Gaus- sian pulse with a 3-dB bandwidth of 1 GHz. The circuit has a pow