A wideband track-and-hold amplifier (THA) for high-speed sampling in analog front-end (AFE) is designed and fabricated in a 0.8µm indium phosphide (InP) process with 165 GHz cut-off frequency ( f T ). Broadband operation is achieved using an enhanced degenerated Darlington f T -doubler buffer, which is first used in the switched-emitter follower (SEF) sampling architecture. Compared with the traditional f T -doubler structures, the enhanced cascode Darlington f T -doubler structure reduces the "V C E mismatch" between the amplifying transistors. Moreover, it can also achieve higher gain more easily, and provide higher V C E for amplifying transistors, which represents higher f T , p e ak performance. Benefiting from the proposed Darlington f T -doubler buffer, the driving capacity of the input stage is also improved. Besides, capacitive/resistive degeneration is introduced to provide higher bandwidth, which generates a zero to cancel the dominant pole of the THA. Moreover, transmission lines (TLs) at the emitter of cascode stages are adopted to reduce the loss of the sampled signals and the drop in the circuit bandwidth. By these methods, the bandwidth is significantly enhanced. The measurement results show that the THA achieves a bandwidth from DC to 29.8 GHz, exhibiting a 0.181f T bandwidth utilization. At 25-GSa/s sampling rate, a total harmonic distortion (THD) of less than -35 dBc and the maximum spurious-free dynamic range (SFDR) of 52.3 dB are tested. The power consumption of the THA is only 672 mW, exhibiting a competitive performance compared with other advanced THAs.

A broadband static frequency divider fabricated in a 165 GHz f t 0.8 µm InP DHBT process is described. Capacitive degeneration technique is adopted, extending the operating bandwidth with little increase in power consumption and area occupancy. The device characteristics are analyzed to achieve high device f t utilization. The chip occupies 0.484 mm×0.44 mm and consumes 380 mW from dual supplies of −2.5 V and −3.5 V. The measured input-referred self-oscillation frequency (SOF) is 56 GHz, and the output power locates in −5.87∼1.87 dBm. With single-ended sinewave input, the divider is operational in 2∼62 GHz, exhibiting a 0.36f t frequency range.

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