ADCs Sample IFs With 14-b Resolution

May 18, 2011
Microwave communications systems rely on high-speed analog-to-digital converters (ADCs) at the beginning of the digital-signal-processing (DSP) chain. Because they are an essential component in most high-frequency receiverstypically ...

Microwave communications systems rely on high-speed analog-to-digital converters (ADCs) at the beginning of the digital-signal-processing (DSP) chain. Because they are an essential component in most high-frequency receiverstypically following the intermediate- frequency (IF) filtersHittite Microwave has added not just one, but a family of ADCs to their high-frequency analog product lines through their acquisition of the Norwegian data converter company Arctic Silicon Devices. The new HMCAD series of high-speed ADCs include single-channel, dual-channel, and four-channel devices capable of operating at sample rates to 640 msamples/s at 14-b resolution (and 1 GSamples/s at 8 b), making them ideal for high-precision sampling of receiver IF signals. The ADCs, which provide serial LVDs output data, are designed to interface with field-programmable gate arrays (FPGAs) from different suppliers.

The flagship model in terms of speed and resolution is the HMCAD1520, essentially four high-speed ADCs on a chip, housed in a 7 x 7 mm QFn 48-lead package (see figure). The low-power sampler is designed for a +1.8-VDC supply. It operates at 40 to 640 MSamples/s in either a high-speed mode (with 12-b resolution) or a precision mode (with 14-b resolution). The ADC integrates a low-jitter clock divider and crosspoint switches (any input can be assigned to any ADC channel), so the sampling rate is multiplexed across the number of channels, with 640 MSamples/s available for single-channel operation and 160 MSamples/s for each of four channels with 12-b standard resolution. When the precision mode is used for 14-b resolution, the maximum sampling rate for four-channel operation is 105 MSamples/s. A serial control interface (SPI) allows operators to instantaneously select operating modes.

The dynamic performance for the HMCAD1520 includes signal-to-noise ratio (SNR) of 70 dB and spurious-free dynamic range (SFDR) of 65 dB at 12-b resolution. The effective number of bits (ENOB) in high-speed mode are 10 b at 640 msamples/s with single-channel operation, 10.6 b at 320 msamples/s with dual-channel operation, and 10.8 b at 160 msamples/s with quad-channel operation. At the higher 14-b resolution, the SNR is 74.5 dB and SFDR is 85 dB for a sampled signal of 70 mHz, with SNR of 74 dB and SFDR of 80 dB for a sampling input signal of 140 mHz. The ENOB performance in precision mode is 11.8 b at sampling rates of either 80 or 105 MSamples/s with a 70 MHz input signal. The differential nonlinearity (DNL) for the HMCAD1520 is rated as 0.2 least significant bit (LSB), while the integral nonlinearity for the ADC is 0.6 LSB for a 70-mHz input at 160 MSamples/s with 12-b resolution. All this performance is available with power consumption of just 490 mW (272 mA at +1.8 VDC) at 640 MSamples/s.

Additional ADCs include model HMCAD1510 with 8-b resolution to 500 msamples/s for one channel and 125 msamples/s for each of four channels; and model HMCAD1511 with 8-b resolution to 1 GSamples/s for single-channel operation and to 250 MSamples/s for each of four channels. They are also supplied in 7 x 7 mm plastic leadless surface-mount packages. The product line also includes the three octal ADCs, housed in 9 x 9 mm plastic leadless surface-mount packages, including model HMCAD1102 with selectable 12- or 13-b resolution at sampling rates to 80 MSamples/s across eight channels.

The ADC line includes models HMCAD1050-40/80 and HMCAD1051-40/80 (dual and single 13-b devices, respectively), with sampling rates to 80 MSamples/s; and models HMCAD1040-40/80 and HMCAD1041-40/80 (dual and single 10-b devices, respectively), with sampling rates to 80 MSamples/s. These ADCs are supplied in 6 x 6 mm plastic leadless surface mount packages. The company is currently offering samples and evaluation kits.

About the Author

Jack Browne | Technical Contributor

Jack Browne, Technical Contributor, has worked in technical publishing for over 30 years. He managed the content and production of three technical journals while at the American Institute of Physics, including Medical Physics and the Journal of Vacuum Science & Technology. He has been a Publisher and Editor for Penton Media, started the firm’s Wireless Symposium & Exhibition trade show in 1993, and currently serves as Technical Contributor for that company's Microwaves & RF magazine. Browne, who holds a BS in Mathematics from City College of New York and BA degrees in English and Philosophy from Fordham University, is a member of the IEEE.

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