A 2-GHz Bandwidth, 0.25-1.7 ns True-Time-Delay Element Using a Variable-Order All-Pass Filter Architecture in 0.13 \mu m CMOS

An all-pass filter architecture that can be generalized to high orders, and can be realized using active circuits is proposed. Using this, a compact true-time-delay element with a widely tunable delay and a large delay-bandwidth product (DBW) is demonstrated. This is useful for beamforming and equalization in the lower GHz range where the use of LC or transmission line-based solutions to realize large delays is infeasible. Coarse tuning of delay is realized by changing the filter's order while keeping the bandwidth constant and fine tuning is implemented by changing the filter's bandwidth utilizing the delay-bandwidth tradeoff. A test chip fabricated in 0.13 \mu \text{m} CMOS process demonstrates a delay tuning range of 250 ps-1.7-ns, over a bandwidth of 2 GHz, while maintaining a magnitude deviation of ±0.7 dB. The filter achieves a DBW of 3.4 and a delay per unit area of 5.8 \mathrm {ns/mm^{2}}. The filter has a worst case noise figure of 23 dB, and -40 dB intermodulation (IM3) distortion for 37 mVppd inputs. The chip occupies an active area of 0.6 mm2, and dissipates 112 mW-364 mW of power between its minimum and maximum delay settings. Computed radiation pattern with four antennas spaced \mathrm {\lambda -{fmax}}/2 apart shows ±90° beam steering off broadside.