Toke Meyer Andersen

A 3.1 mW 8b 1.2 GS/s Single-Channel Asynchronous SAR ADC With Alternate Comparators for Enhanced Speed in 32 nm Digital SOI CMOS

Next-generation digital high-speed links require fast, yet energy-efficient ADCs at minimum area. Recent years saw impressive progress in SAR ADC designs towards higher sampling speed. Asynchronous clocking, redundant capacitive DACs (CDAC), multi-bit decisions per step and interleaved designs have been presented. We present an asynchronous redundant single-channel ADC achieving 1.2GS/s at 1V supply by using two comparators in alternation to relax comparator reset timing. The ADC achieves 39.3dB SNDR and 34fJ/conversion-step with a core chip area of 0.0015mm2.

22.1 A 90GS/s 8b 667mW 64× interleaved SAR ADC in 32nm digital SOI CMOS

Forthcoming optical communication standards such as ITU OTU-4 and 100/400Gb/s Ethernet require ADCs with more than 50GS/s and at least 5 ENOB to enable complex equalization in the digital domain. SAR ADCs and interleaved ADCs made impressive progress in recent years. First CMOS ADCs with at least 6b and conversion rates exceeding 20GS/s were presented, proving that interleaved SAR ADCs are an optimal choice for high-speed ADCs with moderate resolution. We present an interleaved CMOS ADC architecture based on an asynchronous redundant SAR ADC core element. It was measured up to a sampling rate of 100GS/s and can be operated from a single supply voltage. At 90GS/s, the measured SNDR stays above 36.0dB SNDR up to 6.1GHz and 33.0dB up to 19.9GHz input frequency while consuming 667mW. The ADC is implemented in 32nm digital SOI CMOS and occupies 0.45mm2.

20.3 A feedforward controlled on-chip switched-capacitor voltage regulator delivering 10W in 32nm SOI CMOS

On-chip (or fully integrated) switched-capacitor (SC) voltage regulators (SCVR) have recently received a lot of attention due to their ease of monolithic integration. The use of deep trench capacitors can lead to SCVR implementations that simultaneously achieve high efficiency, high power density, and fast response time. For the application of granular power distribution of many-core microprocessor systems, the on-chip SCVR must maintain an output voltage above a certain minimum level Uout, min in order for the microprocessor core to meet setup time requirements. Following a transient load change, the output voltage typically exhibits a droop due to parasitic inductances and resistances in the power distribution network. Therefore, the steady-state output voltage is kept high enough to ensure VOUT >Vout, min at all times, thereby introducing an output voltage overhead that leads to increased system power consumption. The output voltage droop can be reduced by implementing fast regulation and a sufficient amount of on-chip decoupling capacitance. However, a large amount of on-chip decoupling capacitance is needed to significantly reduce the droop, and it becomes impractical to implement owing to the large chip area overhead required. This paper presents a feedforward control scheme that significantly reduces the output voltage droop in the presence of a large input voltage droop following a transient event. This in turn reduces the required output voltage overhead and may lead to significant overall system power savings.

A 10 Gb/s 8-Tap 6b 2-PAM/4-PAM Tomlinson–Harashima Precoding Transmitter for Future Memory-Link Applications in 22-nm SOI CMOS

Tomlinson-Harashima (TH) precoding is a transmitter equalization technique in which the post-cursor intersymbol interference (ISI) is canceled by means of an infinite impulse response (IIR) filter with modulo (MOD)-based amplitude limitation. TH equalizers are suited for asymmetric links, such as DRAM interfaces, where the transmitter contains the equalization complexity and the receiver is kept simple. To increase the data rate, we propose the application of pipelining and half-rate operation to the ISI subtraction in the equalizers feedback path. A TH equalizer with 8 taps, 6 bit resolution, and 2-PAM/4-PAM support has been implemented in 22-nm silicon-on-insulator (SOI) CMOS technology. In measurements, the feedback delay reduction techniques allow us to equalize 34-cm-long PCB traces having 12-dB loss with 7 × ISI reduction for 5.0-Gb/s 2-PAM signaling, and in 10.0-Gb/s 4-PAM mode completely closed eye diagrams are opened. The measured efficiency of the 145 μm× 115 μm transmitter is 1.2 pJ/bit in 4-PAM mode at 5.0 Gbaud with disabled equalization and increases linearly with 14 μW/Gbaud per 1% increase of the equalization tap weights.

Implementation of Low-Power 6–8 b 30–90 GS/s Time-Interleaved ADCs With Optimized Input Bandwidth in 32 nm CMOS

A model for voltage-based time-interleaved sampling is introduced with two implementations of highly interleaved analog-to-digital converters (ADCs) for 100 Gb/s communication systems. The model is suitable for ADCs where the analog input bandwidth is of concern and enables a tradeoff between different architectures with respect to the analog input bandwidth, the hold time of the sampled signal, and constraints on the clock path. The two ADCs at 6 and 8 b resolution implement inline demux sampling with 32χ and 64χ interleaving to achieve 36 GS/s at 110 mW and 90 GS/s at 667 mW, respectively. The analog input bandwidth of both ADCs exceeds 20 GHz. The SNDR of the 64χ interleaved ADC is above 36 dB up to 6.1 GHz and above 33 dB up to 19.9 GHz at 90 GS/s, and the SNDR of the 32χ interleaved ADC exceeds 31.6 dB up to Nyquist at 36 GS/s. The 32χ and 64χ interleaved ADCs are optimized for area and occupy 0.048 and 0.45 mm2, respectively, in 32 nm CMOS SOI technology.

10.6 continuous-time linear equalization with programmable active-peaking transistor arrays in a 14nm FinFET 2mW/Gb/s 16Gb/s 2-Tap speculative DFE receiver

The authors report the implementation of a continuous-time linear equalizer (CTLE) featuring a new technique to control the high-frequency gain peaking and to interface to current-summing stages usually implemented as interleaved slices for the linear analog superposition of the coefficients of decision-feedback equalizers (DFE). The circuits are implemented in 14nm FinFET SOI CMOS technology and are included in a prototype receiver targeted to 16Gb/s serial I/O links for multi-core microprocessors off-chip communication. The architecture is shown in the paper. Power efficiency and compactness are among the primary goals of the study together with an equalization capability sufficient to recover at bit-error rate (BER) levels below 10-12 data transmitted across smooth channels with losses in excess of 25dB at 8GHz.

A 16 Gb/s 3.7 mW/Gb/s 8-Tap DFE Receiver and Baud-Rate CDR With 31 kppm Tracking Bandwidth

A 16 Gb/s I/O link receiver fabricated in 22 nm CMOS SOI technology is presented. Attenuation and ISI of transmitted NRZ data across PCB channels are equalized with a CTLE feeding an 8-tap DFE. The first tap uses digital speculation and the following seven taps are realized by means of the switched-capacitor technique. Timing recovery and control are performed with a Mueller-Müller type-A baud-rate CDR. The architecture is half-rate and requires one phase rotator. In total, each slice has six comparators to recover data and timing information. The secondorder digital CDR operates at quarter-rate and features a low-latency implementation of the proportional path. At 16 Gb/s, 1 Vppd PRBS31 data transmitted without FFE equalization is recovered across a PCB channel with 34 dB attenuation at 8 GHz. The measured tracking bandwidth is 31 kppm (16 GHz ± 496 MHz), and an amplitude of 3 UIPP is tolerated at 1 MHz sinusoidal jitter. The sinusoidal jitter amplitude tolerance measured at 10 Gb/s is 0.4 UIPP at 10 MHz and remains above 0.2 UIPP up to 1 GHz with PRBS31 data recovered (BER <; 10-12) across a PCB channel with 27 dB attenuation at 5 GHz. The power efficiency is 3.7 mW/Gb/s, including the full-rate clock receiver.

A 3.6pJ/b 56Gb/s 4-PAM receiver with 6-Bit TI-SAR ADC and quarter-rate speculative 2-tap DFE in 32 nm CMOS

This paper describes the implementation of a 4-level pulse-amplitude-modulation (4-PAM) receiver consisting of a 6-bit time-interleaved successive-approximation analog-to-digital converter (TI-SAR ADC), followed by a fully digital speculative 2-tap decision-feedback equalizer (DFE) operating at one-fourth of the modulation rate. The receiver, implemented in an experimental chip fabricated in 32 nm SOI CMOS, is designed to recover data at 56Gb/s over a channel with an attenuation of 11 dB at 14 GHz. The power consumption of the receiver is 202.7 mW at a supply of 1.2 V, achieving an overall energy efficiency of 3.62 pJ/b. The DFE along with area-optimized register arrays and memory-control buffers occupies an area of 0.154×0.169 mm2. Experimental results demonstrating a BER<;10-8 are obtained using a (27-1)-bit pseudo-random binary sequence (PRBS-7).

An 8Gb/s 1.5mW/Gb/s 8-tap 6b NRZ/PAM-4 Tomlinson-Harashima precoding transmitter for future memory-link applications in 22nm CMOS

Memory links use variable-impedance drivers, feed-forward equalization (FFE) [1], on-die termination (ODT) and slew-rate control to optimize the signal integrity (SI). An asymmetric DRAM link configuration exploits the availability of a fast CMOS technology on the memory controller side to implement powerful equalization, while keeping the circuit complexity on the DRAM side relatively simple. This paper proposes the use of Tomlinson Harashima precoding (THP) [2-4] in a memory controller as replacement of the afore-mentioned SI optimization techniques. THP is a transmitter equalization technique in which post-cursor inter-symbol interference (ISI) is cancelled by means of an infinite impulse response (IIR) filter with modulo-based amplitude limitation; similar to a decision feedback equalizer (DFE) on the receive side. However, in contrast to a DFE, THP does not suffer from error propagation.

A 16Gb/s 3.7mW/Gb/s 8-tap DFE receiver and baud rate CDR with 30kppm tracking bandwidth

The circuit presented is a power-efficient implementation of a 16 Gb/s I/O link NRZ receiver in 22 nm CMOS SOI. A CTLE feeds an 8-tap DFE for ISI equalization. The first tap uses digital speculation and the following seven taps are realized with switched-capacitor technique. Timing recovery and control are performed with a Mueller-Müller type-A baud rate CDR. The receiver architecture is half rate and requires only a single phase rotator. In total, six comparators in each even/odd signal path slice recover both data and timing information. The timing information extraction requires four additional comparators per slice in parallel to the two required by the first-tap DFE speculation. The CDR digital section operates at quarter rate and features a low-latency implementation for the timing control loop. At 16 Gb/s, 1 Vppd PRBS31 data transmitted without FFE equalization are recovered error-free (BER <; 10-12) across a PCB channel with 34 dB attenuation at 8 GHz. The measured tracking bandwidth is 30 kppm (16 GHz ±480 MHz), and an amplitude of 3 UIPP is tolerated at 1 MHz sinusoidal jitter. The sinusoidal jitter amplitude tolerance measured at 10 Gb/s is 0.4 UIPP at 10 MHz and remains above 0.2 UIPP up to 1 GHz with PRBS31 data recovered error-free (BER<; 10-12) across a PCB channel with 27 dB attenuation at 5 GHz. The power efficiency is 3.7 mW/Gb/s, including the full-rate clock receiver.