A 40-GHz-bandwidth, 4-bit, time-interleaved A/D converter using photoconductive sampling

GaAs photoconductive switches have been integrated with two parallel 4-bit CMOS analog-to-digital (A/D) converter channels to demonstrate the time-interleaved sampling of wideband signals. The picosecond sampling aperture provided by low-temperature-grown-GaAs metal-semiconductor-metal switches, in combination with low-jitter short-pulse lasers, enables the optically-triggered sampling of electrical signals with tens of gigahertz bandwidth at low to medium resolution. A pair of parallel sampling paths, one for sampling and the second for feedthrough cancellation, generate a differential held signal that is quantized by a low-input capacitance, high-speed flash A/D converter. Dynamic offset averaging is employed to improve converter linearity. An experimental time-interleaved two-channel A/D converter provides about 3.5 effective bits of resolution for inputs up to 40 GHz when tested at an optically-triggered sampling rate of 160 MHz. The sampling rate was limited by the available optical source. Each A/D converter channel operates up to a 640-MHz conversion rate, dissipates 70 mW of power, and occupies an area of 150 /spl mu/m /spl times/ 450 /spl mu/m in a 2.5-V, 0.25-/spl mu/m CMOS technology.     

A 5-bit building block for 20 MHz A/D converters

Describes a monolithic, fully parallel 5-bit A/D converter. The chip is fabricated using a standard metal-gate enhancement depletion NMOS technology with 7 /spl mu/m minimum features. The chip contains 31 strobed comparators, latches, combinational logic, a 5/spl times/31 bit ROM, TTL buffers and a 4-bit DAC. This makes it a building block for two-step parallel 8-bit A/D converters. Maximum conversion rate is 20 MHz and DC linearity is better than /SUP 1///SUB 4/ LSB for 80 mV quantization step size.     

An Inherently Monotonic 7-Bit CMOS ADC for Video Applications

This paper describes a CMOS 7-bit flash analog-to-digital converter capable of operation at sample rates in excess of 30 megasamples per second (MSPS) with an analog bandwidth to /spl plusmn/1/2 least significant bit (Isb) of 5 MHz. The device has been realized on a 2-/spl mu/m double-layer metal CMOS process and takes advantage of the low power consumption available from CMOS logic. Circuit techniques have been employed to overcome most of the major problems inherent in flash converters and to guarantee a completely monotonic transfer function.     

A wide input bandwidth 7-bit 300-MSample/s folding and current-mode interpolating ADC

A 7-bit Nyquist folding and interpolating analog-to-digital converter (ADC) that converts at 300 MSamples/s is presented. Using current-mode signal processing techniques for analog preprocessing and a front-end sample-and-hold, the proposed 7-bit folding and interpolating ADC yields a wide input bandwidth up to 60 MHz with six effective number of bits. The ADC consumes 200 mW from a 3.3-V power supply. The chip occupies 1.2 mm/sup 2/ active area, fabricated in 0.35-/spl mu/m CMOS.     

An 80-MHz 8-bit CMOS D/A converter

A high-speed 8-bit D/A converter has been fabricated in a 2-/spl mu/m CMOS technology. In order to achieve high accuracy, a current-cell matrix configuration and a switching sequence called symmetrical switching have been used. The mismatch problem of small-size transistors has been relaxed by this matrix configuration. The linearity error caused by an undesirable current distribution of the current sources has been reduced by symmetrical switching. A high-speed decoding circuit and a fast-setting current source have been developed. The experimental results show that the maximum conversion rate is 80 MHz, a typical DC integral linearity error is 0.38 LSB, a typical DC differential linearity error is 0.22 LSB, and the maximum power consumption is 145 mW. The chip size is 1.85 mm/spl times/2.05 mm.     

A wide-band 280-MHz four-path time-interleaved bandpass sigma-delta modulator

This paper describes a 0.35-/spl mu/m CMOS fourth-order bandpass analog-digital sigma-delta (/spl Sigma//spl Delta/) modulator for wide-band base stations receivers. The modulator, based on a time-interleaved four-path architecture, achieves an equivalent sampling frequency of 280 MHz, although the building blocks operate at only 70 MHz. In measurements, the prototype chip achieves a dynamic range of 72 dB (12 bits of resolution) with a signal bandwidth of 4.375 MHz centered around an intermediate frequency of 70 MHz. The measured spurious-free dynamic range is 69 dB. The /spl Sigma//spl Delta/ modulator dissipates 480 mW from a 3.3-V supply, including voltage reference buffers and output pads with high-driving capabilities, and occupies 20 mm/sup 2/ of silicon area.     

A 3-mW 74-dB SNR 2-MHz continuous-time delta-sigma ADC with a tracking ADC quantizer in 0.13-/spl mu/m CMOS

A third-order continuous-time multibit (4 bit) /spl Delta//spl Sigma/ ADC for wireless applications is implemented in a 0.13-/spl mu/m CMOS process. It is shown that the power consumption can be considerably reduced by using a tracking ADC composed of three comparators with interpolation instead of using a 4-bit flash quantizer. Moreover, the usage of a tracking ADC opens the door to a new forward-looking dynamic element matching (DEM) technique, which helps to reduce the loop delay time and consequently improves the loop stability. The SNR is 74 dB over a bandwidth of 2 MHz. The ADC consumes 3 mW from a 1.5-V supply when clocked at 104 MHz. The active area is 0.3 mm/sup 2/.     

An untrimmed D/A converter with 14-bit resolution

Describes a monolithic 14-bit DAC which uses a new compensation technique for the DAC linearity, the `self-compensation technique', originated through a new concept. Since this technique automatically compensates for linearity error in the DAC by referring to a ramp function with about 17-bit linearity, a high precision DAC can be produced in monolithic form without the trimming of analog components. An experimental 14-bit DAC chip has been fabricated using analog compatible IIL technology and two-level metalization. A linearity error of less that /spl plusmn/1/2 LSB and a settling time of 1-2 /spl mu/s has been achieved.     

A time-interleaved continuous-time /spl Delta//spl Sigma/ modulator with 20-MHz signal bandwidth

This paper presents the first implementation results for a time-interleaved continuous-time /spl Delta//spl Sigma/ modulator. The derivation of the time-interleaved continuous-time /spl Delta//spl Sigma/ modulator from a discrete-time /spl Delta//spl Sigma/ modulator is presented. With various simplifications, the resulting modulator has only a single path of integrators, making it robust to DC offsets. A time-interleaved by 2 continuous-time third-order low-pass /spl Delta//spl Sigma/ modulator is designed in a 0.18-/spl mu/m CMOS technology with an oversampling ratio of 5 at sampling frequencies of 100 and 200 MHz. Experimental results show that a signal-to-noise-plus-distortion ratio (SNDR) of 57 dB and a dynamic range of 60 dB are obtained with an input bandwidth of 10 MHz, and an SNDR of 49 dB with a dynamic range of 55 dB is attained with an input bandwidth of 20 MHz. The power consumption is 101 and 103 mW, respectively.     

A 1.5 V CMOS 4-bit microcomputer needs only 100 /spl mu/W

Describes a new 4-bit microcomputer fabricated using a low-power silicon gate CMOS process and working from a supply voltage down to 1.2 V. The /spl mu/C can directly drive up to seven 3:1 multiplexed LCD digits, scan up 48 keys, and perform 4-bit handshaking data transfer with external devices. 16-bit, single-word instructions and eight stack levels permit efficient use of the 640-word ROM. Operating from a 4.19 MHz crystal, the device has an instruction cycle time of 15 /spl mu/s. An operating power of 100 /spl mu/W at 1.5 W makes the chip ideal for performing control and timing functions in battery operated applications.     

A 10-bit 44-MS/s 20-mW configurable time-interleaved pipeline ADC for a dual-mode 802.11b/Bluetooth receiver

This work presents a configurable time-interleaved pipeline architecture as an efficient solution for the ADC design in high data rate multi-standard radios. The ADC is implemented in a 0.25-/spl mu/m BiCMOS process as part of an integrated dual mode 802.11b/Bluetooth direct conversion receiver. Its structure can be configured to accommodate the different sampling rate and dynamic range requirements of both standards. The different techniques employed at the system and circuit levels to optimize the power consumption are described. An on-line digital calibration scheme is also incorporated to assure the conversion linearity and reduce mismatch among the parallel branches. The proposed ADC is a switched-capacitor implementation occupying an area of 2.1 mm/sup 2/. It achieves 60 dB/64 dB dynamic range at 44 MHz/11 MHz sampling frequency with a power consumption of 20.2 mW/14.8 mW for the 802.11b/Bluetooth baseband signals.     

A 14-bit monotonic NMOS D/A converter

A new configuration of a 14-bit digital-to-analog (D/A) converter has been fabricated as an experimental monolithic NMOS chip. The concept utilizing two cascaded resistor strings delivers an inherent 14 bit monotonicity and a static voltage output signal. The small chip size of about 8.5 mm/SUP 2/ and the saving of external components make the converter applicable for low-cost high-resolution control loop systems. A modified test chip is also described which has been provided as a step into the field of accurate monolithic converters needed for digital audio systems. A voltage output settling time less than 10 /spl mu/s and a linearity at the 12 bit level have been achieved.     

A 95-dB linear low-power variable gain amplifier

An all-CMOS variable gain amplifier (VGA) that adopts a new approximated exponential equation is presented. The proposed VGA is characterized by a wide range of gain variation, temperature-independence gain characteristic, low-power consumption, small chip size, and controllable dynamic gain range. The two-stage VGA is fabricated in 0.18-/spl mu/m CMOS technology and shows the maximum gain variation of more than 95 dB and a 90-dB linear range with linearity error of less than /spl plusmn/ 1 dB. The range of gain variation can be controlled from 68 to 95 dB. The P1dB varies from - 48 to - 17 dBm, and the 3-dB bandwidth is from 32 MHz (at maximum gain of 43 dB) to 1.05 GHz (at minimum gain of - 52 dB). The VGA dissipates less than 3.6 mA from 1.8-V supply while occupying 0.4 mm/sup 2/ of chip area excluding bondpads.     

A CMOS 15-bit 125-MS/s Time-Interleaved ADC With Digital Background Calibration

A 15-bit 125-MS/s two-channel time-interleaved pipelined ADC is fabricated in a 0.18 mum CMOS technology, and achieves 91.9 dB SFDR, 69.9 dB SNDR for a 9.99 MHz input. This ADC incorporates a single sample-and-hold amplifier which employs a precharged circuit configuration to mitigate performance requirements for its opamp. Digital background calibration is applied to maintain the conversion linearity of each A/D channel and also correct both gain and offset mismatches between the two channels. Excluding I/O buffers, the chip occupies an area of 4.3 times 4.3 mm² and dissipates 909 mW from a 1.8 V supply.     

A highly integrated analog front-end for 3G

This paper describes a reconfigurable analog front-end (AFE) and audio codec IC supporting the wideband code division multiple access (WCDMA) standard. The chip is fabricated on Intel's 0.18-/spl mu/m (SOC) flash+logic+analog (FLA) process technology using a 0.35-/spl mu/m feature size analog transistor. The transmit path contains a 10-bit segmented rail-to-rail digital-to-analog converter, automatically tunable active RC filter, and programmable gain amplifier (PGA) with self-tuning gain and offset correction circuit. The receive path incorporates a PGA, active RC filter, and an 8-bit analog-to-digital converter with built-in offset correction. The AFE operates at 2.7 V with a current consumption of 55 mA and total active area of 15 mm/sup 2/.     

Implementation of a third-generation 1.1-GHz 64-bit microprocessor

This third-generation 1.1-GHz 64-bit UltraSPARC microprocessor provides 1-MB on-chip level-2 cache, 4-Gb/s off chip memory bandwidth, and a new 200 MHz JBus interface that supports one to four processors. The 87.5-million transistor chip is implemented in a seven-layer-metal copper 0.13-/spl mu/m CMOS process and dissipates 53 W at 1.3 V and 1.1 GHz.     

An 8-bit 100-MHz CMOS linear interpolation DAC

An 8-bit 100-MHz CMOS linear interpolation digital-to-analog converter (DAC) is presented. It applies a time-interleaved structure on an 8-bit binary-weighted DAC, using 16 evenly skewed clocks generated by a voltage-controlled delay line to realize the linear interpolation function. The linear interpolation increases the attenuation of the DAC's image components. The requirement for the analog reconstruction filter is, therefore, greatly relaxed. The DAC aims for the single-chip integration of a wireless transmitter. The chip was fabricated in a 3.3-V 0.35-/spl mu/m double-poly triple-metal CMOS process. The core size of the chip is 0.67 mm /spl times/ 0.67 mm, and the total power consumption is 54.5 mW with 3.3-V power supplies. The attenuation (in decibels) of image components is doubled compared with a conventional DAC.     

A multibit sigma-delta ADC for multimode receivers

A 2.7-V sigma-delta modulator with a 6-bit quantizer is fabricated in a 0.18-/spl mu/m CMOS process. The modulator makes use of noise-shaped dynamic element matching (DEM) and quantizer offset chopping to attain high linearity over a wide bandwidth. The DEM algorithm is implemented in such a way as to minimize additional delay within the feedback loop of the modulator, thereby enabling the use of the highest resolution quantizer yet reported in a multibit sigma-delta analog-to-digital converter of this speed. The part achieves 95-dB peak spurious-free dynamic range and 77-dB signal-to-noise ratio over a 625-kHz bandwidth, and consumes 30 mW at a sampling frequency of 23 MHz. The part achieves 70-dB signal-to-noise ratio over a 1.92-MHz bandwidth and dissipates 50 mW when clocked at 46 MHz.     

A cascaded continuous-time /spl Sigma//spl Delta/ Modulator with 67-dB dynamic range in 10-MHz bandwidth

This paper presents the design of a 2-2 cascaded continuous-time sigma-delta modulator. The cascaded modulator comprises two stages with second-order continuous-time resonator loopfilters, 4-bit quantizers, and feedback digital-to-analog converters. The digital noise cancellation filter design is determined using continuous-time to discrete-time transformation of the sigma-delta loopfilter transfer functions. The required matching between the analog and digital filter coefficients is achieved by means of simple digital calibration of the noise cancellation filter. Measurement results of a 0.18-/spl mu/m CMOS prototype chip demonstrate 67-dB dynamic range in a 10-MHz bandwidth at 8 times oversampling for a single continuous-time cascaded modulator. Two cascaded modulators in quadrature configuration provide 20-MHz aggregate bandwidth. Measured anti-alias suppression is over 50 dB for input signals in the band from 150 to 170 MHz around the sampling frequency of 160 MHz.     

A 1.5-V 14-bit 100-MS/s self-calibrated DAC

Large-area current source arrays are widely used in current-steering digital-to-analog converters (DACs) to statistically maintain a required level of matching accuracy between the current sources. This not only results in large die size but also in significant degradation of dynamic range for high-frequency signals. To overcome technology barriers, relax requirements on the layout, and reduce DAC sensitivities to process, temperature, and aging, calibration is emerging as a viable solution for the next-generation high-performance DACs. In this paper, a new foreground calibration technique suitable for very-low-voltage environments is presented which effectively compensates for current source mismatch, and achieves high linearity with small die size and low power consumption. Settling and dynamic performance are also improved due to a dramatic reduction of parasitic effects. To demonstrate this technique, a 14-bit DAC prototype was implemented in a 0.13-/spl mu/m digital CMOS process. This is the first CMOS DAC reported that operates with a single 1.5-V power supply and achieves 14-bit linearity with less than 0.1 mm/sup 2/ of active area. At 100 MS/s, the spurious free dynamic range is 82 dB (62 dB) for signals of 0.9 MHz (42 MHz) and the power consumption is only 16.7 mW.