Electronic Design

Low-Power ADC Drivers Combine Low Noise And Low Distortion

At 9.6 mA per channel, the ADA4932 and ADA4950 differential analog-to-digital converter (ADC) drivers from Analog Devices offer the industry’s lowest power consumption and the best performance of any ADC drivers operating at 50 mW or less, according to the company.

The ADA4932 combines the low noise and distortion levels required to drive high-performance 10- to 16-bit ADCs found in today’s power-sensitive medical-imaging, wireless-infrastructure, and instrumentation applications, including ultrasound scanners and picocell and femtocell wireless basestations. With fixed-gain options of 1x, 2x, and 3x, Analog Devices has optimized the ADA4950 for use in smaller designs.

These drivers also achieve 95-dB spurious-free dynamic range (SFDR) and true 14-bit performance at 20 MHz, as well as true 12-bit performance out to 50 MHz. They can operate as single-ended-to-differential or differential-to-differential amplifiers. When performing single-ended-to-differential conversion, the amplifiers require no additional signal conditioning, resulting in better ADC performance with no added components.

The ADA4932 integrates the functionality of a number of discrete components to simplify design tasks for engineers while saving board space. Its output common-mode voltage is user-adjustable by means of an internal common-mode feedback loop, allowing the ADA4932 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, Analog Devices says.

With the ADA4932, differential gain configurations are realized with a simple four-resistor external feedback network that determines the amplifier’s closed-loop gain. It is fabricated using the company’s proprietary silicon-germanium (SiGe) complementary bipolar process, enabling it to achieve low distortion and noise while operating at low power consumption. Its low offset and dynamic performance of the suit it for a wide variety of data acquisition and signal processing applications.

Manufactured on the company’s proprietary extra-fast complementary bipolar (XFCB) process, the ADA4950 has a –3-dB bandwidth of 750 MHz and delivers a differential signal with very low harmonic distortion. Users can configure its internal resistor network for gains of 1, 2, and 3 in an otherwise fixed architecture.

An internal common-mode feedback loop provides a balanced output with gain and phase matching and suppresses even-order harmonics. The internal feedback circuit also minimizes 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, maximizing 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. Its distortion performance suits communication systems, while its wide bandwidth and high IP3 also make it desirable for use as a gain block in IF and baseband signal chains.

The single-channel ADA4932-1 and ADA4950-1 come in a 3- by 3-mm, 16-lead lead-frame chip-scale package (LFCSP) and cost $2.95 each in 1000-unit lots. The dual-channel ADA4932-2 and ADA4950-2 come in a 4- by 4-mm, 24-lead LFCSP and cost $5.29 each in 1000-unit lots. All of the drivers are available now.

Analog Devices

www.analog.com

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