ADCs Sample IFs With 14-b Resolution

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.

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