A 1.2 V 10-bit 100 MS/s Successive Approximation (SA) ADC is presented. The scheme achieves high-speed and low-power operation thanks to the reference-free technique that avoids the static power dissipation of an on-chip reference generator. Moreover, the use of a common-mode based charge recovery switching method reduces the switching energy and improves the conversion linearity. A variable self-timed loop optimizes the reset time of the preamplifier to improve the conversion speed. Measurement results on a 90 nm CMOS prototype operated at 1.2 V supply show 3 mW total power consumption with a peak SNDR of 56.6 dB and a FOM of 77 fJ/conv-step.

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A 10-bit 100-MS/s Reference-Free SAR ADC in 90 nm CMOS

A fully-integrated FMCW radar system for automotive applications operating at 77 GHz has been proposed. Utilizing a fractional- synthesizer as the FMCW generator, the transmitter linearly modulates the carrier frequency across a range of 700 MHz. The receiver together with an external baseband processor detects the distance and relative speed by conducting an FFT-based algorithm. Millimeter-wave PA and LNA are incorporated on chip, providing sufficient gain, bandwidth, and sensitivity. Fabricated in 65-nm CMOS technology, this prototype provides a maximum detectable distance of 106 meters for a mid-size car while consuming 243 mW from a 1.2-V supply.

A Fully-Integrated 77-GHz FMCW Radar Transceiver in 65-nm CMOS Technology

i»?The StrongARM latch topology finds wide usage as a sense amplifier, a comparator, or simply a robust latch with high sensitivity. The term âStrongARMâ commemorates the use of this circuit in Digital Equipment Corporationâs StrongARM microprocessor [1], but the basic structure was originally introduced by Toshibaâs Kobayashi et al. [2]. The StrongARM latch has become popular for three reasons: 1) it consumes zero static power, 2) it directly produces rail-to-rail outputs, and 3) its input-referred offset arises from primarily one differential pair. In this column, we study the circuit and its properties.

The StrongARM Latch [A Circuit for All Seasons]

This paper describes an ultra-low power SAR ADC for medical implant devices. To achieve the nano-watt range power consumption, an ultra-low power design strategy has been utilized, imposing maximum simplicity on the ADC architecture, low transistor count and matched capacitive DAC with a switching scheme which results in full-range sampling without switch bootstrapping and extra reset voltage. Furthermore, a dual-supply voltage scheme allows the SAR logic to operate at 0.4 V, reducing the overall power consumption of the ADC by 15% without any loss in performance. The ADC was fabricated in 0.13-μm CMOS. In dual-supply mode (1.0 V for analog and 0.4 V for digital), the ADC consumes 53 nW at a sampling rate of 1 kS/s and achieves the ENOB of 9.1 bits. The leakage power constitutes 25% of the 53-nW total power.

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A 53-nW 9.1-ENOB 1-kS/s SAR ADC in 0.13- $\mu$ m CMOS for Medical Implant Devices

This paper presents a power- and area-efficient 24-way time-interleaved successive-approximation-register (SAR) analog-to-digital converter (ADC) that achieves 2.8 GS/s and 8.1 ENOB in 65 nm CMOS. To minimize the power and the area, the capacitors in the capacitive DAC are sized to meet the thermal noise requirements rather than the matching requirements, leading to the LSB capacitance of 50 aF. An on-chip digital background calibration is used to calibrate the capacitor mismatches in individual ADC channels, as well as the inter-channel offset, gain and timing mismatches. Measurement results at the 2.8 GS/s sampling rate show that the ADC chip prototype consumes 44.6 mW of power from a 1.2 V supply while achieving peak SNDR of 50.9 dB and retaining SNDR higher than 48.2 dB across the entire first Nyquist zone with a 1.8Vpp-diff input signal. The prototype chip occupies an area of 1.03 × 1.66 mm2, including the pads and the testing circuits. The figure of merit (FoM) of this ADC, calculated with the minimum SNDR in the first Nyquist zone, is 76 fJ/conversion-step.

A 2.8 GS/s 44.6 mW Time-Interleaved ADC Achieving 50.9 dB SNDR and 3 dB Effective Resolution Bandwidth of 1.5 GHz in 65 nm CMOS

Rapid growth in the demand for “Green-IT” or medical applications requires power efficient ADCs. SAR ADC power scales with CMOS technology because it does not need operational amplifiers, which are getting difficult to design in deeply scaled CMOS. Recent published SAR ADCs have no static current, which improves energy efficiency [1, 2]. Split capacitor digital-to-analog converter (CDAC) is one of the best architectures for high resolution SAR ADC, but is very sensitive to the splitting capacitor because of its fractional value and parasitic. Conventional SAR ADC needs approximately 10 times faster external clock if it has no internal clock generator. However the internal SAR clock generation enables the external clock frequency to be the same as the sampling rate, but suffers from unstable operation caused by large PVT delay variation. This ADC is designed with on-chip digital calibration techniques, comparator offset calibration, CDAC linearity error calibration and internal clock frequency control to compensate for the PVT variation. The ADC is integrated in 65nm CMOS and achieved 10b at 50MS/s while consuming 820µW from a 1.0V supply.

A 10b 50MS/s 820µW SAR ADC with on-chip digital calibration

A split capacitor DAC calibration method is proposed that a bridge capacitor larger than conventional design allows a tunable capacitor to compensate for mismatch. To guarantee proper calibration, a comparator with digital timing control offset cancellation is proposed. An 8-bit successive approximation ADC with 4b+4b split capacitor DAC calibration has been implemented in 65nm CMOS, achieving 0.3LSB DNL and INL with 180fF input capacitance.

Split capacitor DAC mismatch calibration in successive approximation ADC

This 10-b 50-MSamples/s SAR analog-to-digital converter (ADC) features on-chip digital calibration techniques, comparator offset cancellation, a capacitor digital-to-analog converter (CDAC) linearity calibration, and internal clock control to compensate for PVT variations. A split-CDAC reduces the exponential increase in the number of unit capacitors needed and enables the input load capacitance to be as small as the kT/C noise restriction. The prototype fabricated in 65 nm 1P7M complementary metal-oxide semiconductor with MIM capacitor achieves 56.6 dB SNDR at 50-MSamples/s, 25-MHz input frequency and consumes 820 μW from a 1.0-V supply, including the digital calibration circuits. The figure of merit was 29.7 fJ/conversion-step under the Nyquist condition. The ADC occupied an active area of 0.039 mm2 .

A 10-b 50-MS/s 820- $\mu $ W SAR ADC With On-Chip Digital Calibration

Charge redistribution based successive approximation (SA) analog-to-digital converter (ADC) has the advantage of power efficiency. Split capacitor digital-to-analog converter (CDAC) technique implements two sets of binary-weighted capacitor arrays connected by a bridge capacitor so as to reduce both input load capacitance and area. However, capacitor mismatches degrade ADC performance in terms of DNL and INL. In this work, a split CDAC mismatch calibration method is proposed. A bridge capacitor larger than conventional design is implemented so that a tunable capacitor can be added in parallel with the lower-weight capacitor array to compensate for mismatches. To guarantee correct CDAC calibration, comparator offset is cancelled using a digital timing control charge compensation technique. To further reduce the input load capacitance, an extra unit capacitor is added to the higher-weight capacitor array. Instead of the lower-weight capacitor array, the extra unit capacitor and the higher-weight capacitor array sample analog input signal. An 8-bit SA ADC with 4-bit + 4-bit split CDAC has been implemented in a 65nm CMOS process. The ADC has an input capacitance of 180fF and occupies an active area of 0.03mm2. Measured results of +0.2/-0.3LSB DNL and +0.3/-0.3LSB INL have been achieved after calibration.

Split Capacitor DAC Mismatch Calibration in Successive Approximation ADC

A comparison circuit comprising: an input circuit includes a first transistor for receiving a first signal, and a second transistor for receiving a second signal; a first current route of which the electric current is controlled by the first transistor; a second current route of which the electric current is controlled by the second transistor; a latch for amplifying potential difference between the first current route and the second current route; a comparative operation control circuit including a first switch for executing or blocking supply voltage to the drain of the first transistor, a second switch for executing or blocking supply voltage to the drain of the second transistor, and a third switch for executing supply voltage to the first current route and the second current route; a comparative operation setting circuit for controlling supply or blocking of supply of the first switch, the second switch, and the third switch.

Takeshi Takayama

Papers

A 10b 50MS/s 820µW SAR ADC with on-chip digital calibration

Split capacitor DAC mismatch calibration in successive approximation ADC

A 10-b 50-MS/s 820- $\mu $ W SAR ADC With On-Chip Digital Calibration

Split Capacitor DAC Mismatch Calibration in Successive Approximation ADC

Comparison circuit and analog-to-digital conversion device