Multichannel wireless applications require a generous complement of signal-processing components. To save space and power in such systems, Texas Instruments has packed a line of eight-channel analogto- digital converters (ADCs) in tiny 9 x 9 mm 64-lead QFN-64 housings. The ADS528x line of data converters offers as much as 12-b resolution at sampling rates to 65 MSamples/s with industry-low power consumption.
The ADS528x family includes models ADS5281, ADS5282, and ADS5287. The ADS5281 is the lowest- power member of the trio, with 12-b resolution across eight processing channels at sampling rates to 50 MSamples/s and power consumption of only 64 mW/channel when operating at top sampling speed. The ADS5282 and ADS5287 trade off slightly higher power consumption for higher sampling rates, with the ADS5282 providing 12-b resolution for sampling rates to 65 MSamples/s at power consumption of typically 77 mW/channel and the ADS5287 delivering 10-b resolution at sampling rates to 65 MSamples/s at the same 77 mW/channel power consumption. The power consumption is a function of sampling rate, with the ADS528x converters achieving power dissipation of 48 mW/channel for a sampling rate of 30 MSamples/s, 55 mW/channel at 40 MSamples/s, 64 mW/channel at 50 MSamples/s, and 77 mW/channel at 65 MSamples/s.
All three models are designed for analog supply voltages of +3.0 to +3.6 VDC (typically +3.3 VDC) and digital supply voltages of +1.7 to +1.9 VDC (typically +1.8 VDC). The converters feature an analog input bandwidth of typically 50 MHz and, depending upon model, can be used with clock frequencies from 10 to 65 MHz at a 50-percent duty cycle. They are designed for use with single-ended or differential clocks, and provide serialized low-voltage differential signaling (LVDS) outputs.
Each converter exhibits differential input capacitance of a mere 3 pF and can handle a peak-to-peak differential input voltage range of 2 V. Overload recovery circuitry allows each ADC to provide valid data within one clock cycle after an input overload as high as 6 dB. With programmable digital gain from 0 to 12 dB, full-scale outputs can be provided for input signals as low as 0.5 V peak to peak.
The converters feature a low-frequency noise-suppression mode to minimize 1/f device noise, improving the signal-to-noise ratio (SNR) by as much as 4.2 dB over a 1-MHz bandwidth in baseband applications. For example, for noise integrated from DC to 1 MHz, the ADS5281's SNR with the low-frequency noise-suppression mode disabled is 81.9 dB full scale, improving to 89.2 dB full scale when using the low-frequency noise-suppression mode. For noise integrated from DC to 2 MHz, the ADS5281's SNR with the low-frequency noise-suppression mode disabled is 80.0 dB full scale, improving to 83.3 dB full scale when using the lowfrequency noise-suppression mode.
In support of system-level integration of the new eight-channel converters, the company has introduced an octal (eight-channel) variable-gain amplifier (VGA), model VCA8500, with no extra components needed for connections between the VGA and a data converter. Like the data converters, it is supplied in a 64-pin 9 x 9 mm QFN package. And like the converters, it requires little power, with typical power consumption of 63 mW/channel for an input noise level of 0.8 nV/(Hz)0.5 A combination of the VGA with one of the data converters yields eight channels of signal processing capable of 50 MSamples/s for less than 130 m/channel power consumption.
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