Dong-Young Chang

Design techniques for a pipelined ADC without using a front-end sample-and-hold amplifier

Design techniques for a low-power pipelined analog-to-digital converters (ADC) without using a front-end sample-and-hold amplifier are presented. Two sampling topologies are compared that minimize aperture error by matching the time constant between signal paths. A digital correction expansion technique is also presented for multibit ADCs, which further increases tolerance to aperture error. Elimination of the front-end SHA can save more than half of the ADCs static power dissipation.

A 0.6-V 82-dB delta-sigma audio ADC using switched-RC integrators

A 0.6-V 2-2 cascaded audio delta-sigma ADC is described. It uses a resistor-based sampling technique which achieves high linearity and low-voltage operation without subjecting the devices to large terminal voltages. A low-distortion feed-forward topology combined with nonlinear local feedback results in enhanced linearity by reducing the sensitivity to opamp distortion, and allows increased input amplitude, resulting in higher SNDR. The modulator achieves 82-dB dynamic range and 81-dB peak SNDR in the A-weighted audio signal bandwidth with an OSR of 64. The total power consumption of the modulator is 1 mW from a 0.6-V supply. The prototype occupies 2.9 mm/sup 2/ using a 0.35-/spl mu/m CMOS technology.

A 1.4-V 10-bit 25-MS/s pipelined ADC using opamp-reset switching technique

A low-voltage opamp-reset switching technique (ORST) that does not use clock boosting, bootstrapping, switched-opamp (SO), or threshold voltage scaling is presented. This technique greatly reduces device reliability issues. Unlike the SO technique, the opamps stay active for all clock phases and, therefore, the ORST is suitable for high-speed applications. This new switching technique is applied to the design of a 10-bit 25-MS/s pipelined analog-to-digital converter (ADC). The prototype ADC was fabricated in a 0.35-/spl mu/m CMOS process and demonstrates 55-dB signal-to-noise ratio, 55-dB spurious-free dynamic range, and 48-dB signal-to-noise-plus-distortion ratio performance with a 1.4-V power supply. The total power consumption is 21 mW. The ADCs minimum operating power supply is 1.3 V (|V/sub TH,P/| = 0.9 V) and the maximum operating frequency is 32 MS/s. The ORST is fully compatible with future low-voltage submicron CMOS processes.

Sub-1-V design techniques for high-linearity multistage/pipelined analog-to-digital converters

The design of an ultra-low-voltage multistage (two-stage algorithmic) analog-to-digital converter (ADC) employing the opamp-reset switching technique is described. A highly linear input sampling circuit accommodates truly low-voltage sampling from external input signal source. A radix-based digital calibration technique is used to compensate for component mismatches and reduced opamp gain under low supply voltage. The radix-based scheme is based on a half-reference multiplying digital-to-analog converter structure, where the error sources seen by both the reference and input signal paths are made identical for a given stage. The prototype ADC was fabricated in a 0.18-/spl mu/m CMOS process. The prototype integrated circuit dissipates 9 mW at 0.9-V supply with an input signal range of 0.9 V/sub p-p/ differential. The calibration of the ADC improves the signal-to-noise-plus-distortion ratio from 40 to 55 dB and the spurious-free dynamic range from 47 to 75 dB.

Radix-based digital calibration techniques for multi-stage recycling pipelined ADCs

This work describes a digital-domain self-calibration technique for multistage pipelined analog-to-digital converters (ADCs). By making the signal paths of both the input and the reference voltage the same, all error factors within a stage are merged into a single term which represents the equivalent radix number. The initially estimated radix for each stage mathematically iterates to the final correct value via an incremental update algorithm, after foreground calibration measurements are obtained during ADCs recycling mode of operation. In this way, an accurate calibration is achieved using a modified radix-based calculation. Two different single-bit-per-stage ADC adaptation/calibration methods are presented as examples. The proposed technique compensates for linear errors such as capacitor mismatches as well as finite opamp gain.

A low-Voltage 10-bit CMOS DAC in 0.01-mm/sup 2/ die area

A low-voltage 10-bit digital-to-analog converter (DAC) for static/dc operation is fabricated in a standard 0.18-/spl mu/m CMOS process. The DAC is optimized for large integrated circuit systems where possibly dozens of such DAC would be employed for the purpose of digitally controlled analog circuit calibration. The DAC occupies 110 /spl mu/m/spl times/94 /spl mu/m die area. A segmented R-2R architecture is used for the DAC core in order to maximize matching accuracy for a minimal use of die area. A pseudocommon centroid layout is introduced to overcome the layout restrictions of conventional common centroid techniques. A linear current mirror is proposed in order to achieve linear output current with reduced voltage headroom. The measured differential nonlinearity by integral nonlinearity (DNL/INL) is better than 0.7/0.75 LSB and 0.8/2 LSB for 1.8-V and 1.4-V power supplies, respectively. The DAC remains monotonic (|DNL|<1 LSB) as INL reaches 4 LSB down to 1.3-V operation. The DAC consumes 2.2 mA of current at all supply voltage settings.

A 12 bit 200 MS/s Zero-Crossing-Based Pipelined ADC With Early Sub-ADC Decision and Output Residue Background Calibration

A 12 bit 200 MS/s analog-to-digital converter (ADC) applies techniques of zero-crossing-based circuits as a replacement for high-gain high-speed op-amps. High accuracy in the residue amplifier is achieved by using a coarse phase in ZCBC followed by a level-shifting capacitor for fine phase. Sub-ADC flash comparators are strobed immediately after the coarse phase to achieve a high sampling rate. The systematic offset voltage between the coarse and fine phase manifests itself as systematic offset in the sub-ADC comparators. This offset is caused by the coarse phase undershoot and the fine phase overshoot. In this work, the offset is cancelled with background calibration by residue range correction circuits in the following stages sub-ADC. In addition, the sub-ADCs random comparator offset is calibrated with a discrete-time charge-pump based background calibration technique. The reference buffer, bias circuitry, and digital error correction circuits are all integrated on a single chip. The ADC occupies an area of 0.282 mm 2 in 55 nm CMOS technology and dissipates 30.7 mW. It achieves 64.6 dB SNDR and 82.9 dBc SFDR at 200 MS/s for a FOM of 111 fJ/conversion-step. The SNDR degrades gracefully above the designed sampling frequency to 62.9 dB at 250 MS/s, and remains above 50 dB at 300 MS/s.

A 16-bit 65-MS/s Pipeline ADC With 80-dBFS SNR Using Analog Auto-Calibration in SiGe SOI Complementary BiCMOS

A 16-bit 65-MS/s switched-capacitors pipeline analog-to-digital converter built in 0.45-mum 25-GHz fT complementary silicon-on-insulator BiCMOS delivers 80.1-dBFS signal-to-noise ratio, 98-dBc spurious-free dynamic range (SFDR) with 3-Vpp input range at 2-MHz input frequency. The 5 times 5.3 mm2 die consumes 1.7 W from a dual plusmn2.7-V supply. A noniterative analog auto-calibration algorithm simultaneously compensates for both random mismatch in the capacitors of the first quantizer stages, and integral nonlinearity curvatures contributed by sample-and-hold (S/H) and voltage reference buffers, yielding SFDR optimizations up to 12 dB. The test chip performance validates the transient noise simulations run for the analog front-end and the clock jitter, corroborating the efficacy of the circuit techniques adopted to design S/H, clock and references.

Radix-based digital calibration technique for multi-stage ADC

This paper describes a digital-domain self-calibration technique for a multi-stage analog-to-digital converter (ADC). An accurate calibration is achieved by using a modified radix-based calculation. The equivalent radix-based error term for each stage is extracted by measuring major carry jumps from the ADC transfer curve. A new multiplying digital-to-analog converter (MDAC) architecture using V/sub ref//2 (instead of V/sub ref/) is used to reduce the number of error terms in each stage. The radix-based digital calibration technique calibrates capacitor mismatch as well as finite opamp DC gain, while the digital redundancy compensates for opamp and comparator offsets and signal-independent charge injection.

Low-voltage pipelined ADC using opamp-reset switching technique

A low-voltage opamp-reset switching technique (ORST) which avoids clock boosting/bootstrapping, switched-opamp, and threshold voltage scaling is presented. The switching technique is applied to the design of a 10-bit 25 MSPS pipelined ADC. The prototype ADC demonstrates 55 dB SNR, 55 dB SFDR, and 48 dB SNDR at 1.4 V power supply. The ADC operates down to 1.3 V power supply (|V/sub TH,P/|=0-9 V) with 5 dB degradation in performance. Maximum operating frequency is 32 MSPS. The ORST is fully compatible with future low-voltage submicron CMOS processes.