Pier Andrea Francese

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.

4.7 A sub-ns response on-chip switched-capacitor DC-DC voltage regulator delivering 3.7W/mm 2 at 90% efficiency using deep-trench capacitors in 32nm SOI CMOS

For an on-chip or fully integrated microprocessor power-delivery system, the on-chip power converter must 1) be designed using the same technology as the microprocessor, 2) deliver high power density to supply a microprocessor core with small area overhead, 3) achieve high efficiency, and 4) perform fast regulation over a wide voltage range for dynamic voltage and frequency scaling (DVFS). On-chip switched-capacitor (SC) converters have gained increasing popularity for this application due to their ease of integration using only transistors and capacitors readily available in the chosen technologies [1-6].

A 4.6W/mm 2 power density 86% efficiency on-chip switched capacitor DC-DC converter in 32 nm SOI CMOS

The future trends in microprocessor supply current requirements represent a bottleneck for next generation high-performance microprocessors since the number of supply pins will constitute an increasingly larger fraction of the total number of package pins available. This leaves few pins available for signaling. On-chip power conversion is a means to overcome this limitation by increasing the input voltage - thereby reducing the input current - and performing the final power conversion on the chip itself. This paper details the design and implementation of on-chip switched capacitor converters in deep submicron technologies. High capacitance density deep trench capacitors with a low parasitic bottom plate capacitor ratio available in the technology facilitate high power density and efficiency in on-chip switched capacitor converter implementations. The measured performance of a 2 : 1 voltage conversion ratio on-chip switched capacitor converter implemented in 32nm SOI CMOS technology with 1.8V input voltage results in a power density of 4.6W/mm2 at 86% efficiency when operated at a switching frequency of 100MHz.

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.

A 13-b 1.1-MHz oversampled DAC with semidigital reconstruction filtering

A digital-to-analog converter (DAC) composed of a cascaded digital /spl Sigma//spl Delta/ modulator and the combination of a semidigital/digital finite-impulse response (FIR) and an infinite-impulse response (IIR)-SC/RC filter is described. The architecture enables the analog linear reconstruction of 16/spl times/ oversampled digital signals. With the analog section implemented in CMOS 0.18-/spl mu/m and the digital part programmed into a field-programmable gate array (FPGA), the modulator plus reconstruction filter achieves a peak SNR of 78 dB. The spurious-free dynamic range reaches 80 dB and stays better than 73 dB within the 1.104-MHz signal band. A missing-tone-power ratio of 70 dB, demonstrated for a signal with 15-dB peak-to-average ratio, proves that the solution is suitable for ADSL-CO transmitters.

A 32 Gb/s Backplane Transceiver With On-Chip AC-Coupling and Low Latency CDR in 32 nm SOI CMOS Technology

This paper describes key design features of a 32 Gb/s 4-tap FFE/15-tap DFE transceiver in 32 nm SOI CMOS which mitigate major sources of degradation in transceiver performance. The transceiver employs a passive feed-forward restore (FFR) scheme in an on-chip AC-coupling network to prevent pattern-dependent baseline wander, a low-latency clock and data recovery (CDR) to improve high-frequency jitter tolerance, and a token-based power management scheme to reduce supply ripple. At 32 Gb/s, the transceiver can equalize a channel with 30 dB of loss at a bit-error rate below 10-12 while consuming 21 mW/Gbps at 1 V supply and an area of 0.7 mm2.

A 3.1mW/Gbps 30Gbps quarter-rate triple-speculation 15-tap SC-DFE RX data path in 32nm CMOS

This paper describes a low-power implementation of a receiver data path, consisting of the RX termination with ESD, continuous-time linear equalizer (CTLE), and a 15-tap decision feedback equalizer (DFE) running at quarter rate. While the first 3 DFE taps are implemented by speculation, the latter 12 taps use a switched-cap (SC-DFE) approach. The circuit was produced in 32nm SOI-CMOS, and was measured to receive 30Gb/s PRBS31 data at <;10-12 BER over a 36dB loss channel with an energy efficiency of 3.1mW/Gbps.

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.