Analog Devices extended its family of low-power, low-distortion ADC (analog-to-digital converter) drivers with the introduction of the ADA4932 and ADA4950 differential amplifiers.
The ADA4932 combines the low noise and distortion levels required to drive high-performance 10-bit to 16-bit ADCs found in power-sensitive medical-imaging, wireless-infrastructure and instrumentation applications, including ultrasound scanners and picocell and femtocell wireless base stations. With fixed-gain options of 1x, 2x, and 3x, the ADA4950 is optimised for use in smaller designs. In addition to their low supply current of 9,6 mA per channel, these new drivers achieve 95 dB SFDR (spurious-free dynamic range) and true 14 bit performance at 20 MHz, as well as true 12-bit performance out to 50 MHz.
Both drivers can operate as single-ended-to-differential or differential-to-differential amplifiers. When performing single-ended-to-differential conversion, they require no additional signal conditioning, resulting in enhanced ADC performance with no added components.
The ADA4932’s output common-mode voltage is user-adjustable by means of an internal common-mode feedback loop, allowing its output to match the input of the ADC. The internal feedback loop also provides exceptional output balance as well as suppression of even-order harmonic distortion products. Differential gain configurations are realised with a simple four-resistor external feedback network that determines the amplifier’s closed-loop gain. The low offset and dynamic performance of the ADA4932 make it well suited for a variety of data acquisition and signal processing applications.
The ADA4950 has a –3 dB bandwidth of 750 MHz and delivers a differential signal with very low harmonic distortion. It has an internal resistor network that users can configure for gains of 1, 2 and 3 in an otherwise fixed architecture. The device has an internal common-mode feedback loop that provides a balanced output with gain and phase matching, and suppresses even-order harmonics. The internal feedback circuit also minimises any balance error that would be associated with mismatches in the gain-setting resistors. The ADA4950 driver’s differential output helps balance the input to differential ADCs, maximising the performance of the ADC.
The ADA4950 eliminates the need for a transformer when driving high-performance ADCs, preserving the source signal’s low-frequency and DC information. The common-mode level of the differential output is adjustable by applying a voltage on the VOCM pin, which level-shifts the input signal for driving single-supply ADCs. The amplifier’s fast overload recovery preserves sampling accuracy. The distortion performance of the ADA4950 is attractive for communication systems, while its wide bandwidth and high IP3 also make it suitable for use as a gain block in IF and baseband signal chains.
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