This article presents a 50-112-Gb/s current-mode four-level pulse amplitude modulation (PAM-4) transmitter with a two-tap fractional-spaced feed-forward equalizer (FFE). The principle analysis shows that the fractional-spaced FFE can provide an extended compensation range beyond the Nyquist frequency without amplifying noise. For the transmitter prototype implementation, the tap delay is adjusted by a coarse-fine capacitor array-based delay cell located in the quarter-rate clock path. Dynamic latches, pseudo-AND2s, and bandwidth-enhanced 4:1 multiplexers are employed to guarantee an adequate timing margin and a sufficient bandwidth for the data rate of 112 Gb/s. A linearity-optimized FFE driver is employed to overcome the current compression caused by the channel-length modulation. Fabricated in a 65-nm CMOS process, the measurement results show that the proposed fractional-spaced FFE can significantly improve the eye-opening in terms of expanding the eye width and optimizing the eyelid thickness. The PAM-4 transmitter can operate in both full-rate PAM-4 and half-rate NRZ modes, achieving a maximum data rate of 112 Gb/s with an energy efficiency of 2.17 pJ/bit.

In this letter, we present a 24-GSa/s, >20-GHz wideband track-and-hold amplifier (THA) based on indium phosphide (InP) double-heterojunction bipolar transistor (DHBT) technology for high-speed sampling systems. In the proposed approach, the output pole of the input stage is canceled by the zero produced by the emitter capacitive/resistive degeneration, and the bandwidth is thereby extended without voltage drop. The compensation technique for Vbe modulation in the output stage is introduced to reduce distortion. The monolithic microwave integrated circuit (MMIC) prototype occupies only 0.69 mm², and the experimental results show that it has a 0.112-fT bandwidth from dc to 22.3 GHz, which is wider than any ratio reported compact THA solutions using the InP technology. In addition, a spurious-free dynamic range (SFDR) of better than 42 dB and total harmonic distortion (THD) of less than -25 dBc are demonstrated at a 24-GSa/s sampling rate. The THA consumes only 374 mW, which is among the lowest dc power dissipation reported for the InP technology.

This brief presents a 16-bit 5 GS/s current-steering digital-to-analog converter (DAC) with a redundant-MSB based digital pre-distortion (RMDPD) technique. 1-bit MSB is added during decoding to accommodate digital compensation of element mismatch errors, enhancing both the low-frequency and high-frequency linearity without penalty on the noise floor. In addition, an improved data/dummy-data scheme, which incorporates the dummy-data generation logic into the 2:1 multiplexer (MUX) with half-rate clock, is used to mitigate the code-dependent supply ripples and induced retiming errors. The implemented DAC achieves > 61 dBc spurious-free dynamic range (SFDR) and < -72 dBc third-order intermodulation distortion (IM3) for output frequencies up to Nyquist. The DAC core occupies 0.42 mm2 active area and dissipates about 360 mW at 1.8V/1.0V/-1.8V supply.

To address the problem of low trigger accuracy during trigger resampling and variable sampling rate trigger resampling using a fixed sampling rate analog-to-digital converter (ADC), this paper proposes an interpolation method combining sinc interpolation and linear interpolation to improve accuracy, based on a digital trigger. After behavior simulation verification and actual field programmable gate array (FPGA) test verification, the data collected by two 3GSps 12-bit ADCs were subjected to 8-times sinc interpolation followed by 16-times linear interpolation processing, after which the original trigger resampling accuracy was increased by 128 times and the sampling rate could be realized to vary between 100 MHz and 1 GHz. A signal–noise ratio (SNR) of 46.80 dBFS, a spurious free dynamic range (SFDR) of 45.91 dB, and an effective number of bits (ENOB) of 7.48 bits were obtained by direct trigger resampling without algorithm processing in the behavior simulation. Meanwhile, an SNR of 58.98 dBFS, an SFDR of 60.96 dB, and an ENOB of 9.42 bits were obtained by trigger resampling after algorithm processing. Due to the influence of analog link signal loss and signal interference on the development board, an SNR, SFDR and ENOB of 51.97 dBFS, 61.26 dB, and 8.32 bits, respectively, were obtained from the trigger resampling in the FPGA test. The experimental results show that the algorithm has not only improved the triggering accuracy but has also improved the SNR, SFDR, and ENOB parameters.

This brief presents a current-steering 25-GS/s 8-bit digital-to-analog converter (DAC) based on a 40-nm CMOS technology. The DAC employs a dual-edge sampling (DES) architecture to reduce the requirement of main clock frequency, optimizing switching noise and improving power efficiency. DES is sensitive to the clock duty cycle. To minimize the image tones and performance degradation caused by duty-cycle errors, a single-slope analog-to-digital converter (ADC)-based duty-cycle detection and correction scheme is proposed, achieving closed-loop background calibration. A T-coil output network is used to extend the bandwidth. The proposed DAC achieves a spurious-free dynamic range (SFDR) of >40 dBc up to the Nyquist frequency and a >12-GHz output bandwidth with sinc roll-off compensation. The active power consumption is about 272 mW under 1.8-/0.9-/−1.8-V power supply.