Quad Low Noise, Low Cost Variable Gain Amplifier
The AD8335 is a quad variable gain amplifier (VGA) with low noise preamplifier intended for cost and power sensitive applications. Each channel features a gain range of 48 dB, fully differential signal paths, active input preamplifier matching, and user-selectable maximum gains of 46 dB and 38 dB. Individual gain controls are provided for each channel.
The preamplifier (PrA) has a single-ended to differential gain of ×8 (18.06 dB) and accepts input signals <625 mV p-p. PrA noise is 1.2 nV/√Hz and the combined input referred voltage noise of the PrA and VGA is 1.3 nV/√Hz at maximum gain.
Assuming a 20 MHz noise bandwidth (NBW), the Nyquist frequency for a 40 MHz ADC, the input SNR is 92 dB. The HLxx pin optimizes the output SNR for 10-bit and 12-bit ADCs with 1 V p-p or 2 V p-p full-scale (FS) inputs.
Channel 1 and Channel 2 are enabled through the EN12 pin and Channel 3 and Channel 4 are enabled through the EN34 pin. For VGA only applications, the PrAs can be powered down, significantly reducing power consumption.
The AD8335 is available in a 64-lead lead frame chip scale package (9 mm × 9 mm) for the industrial temperature range of −40°C to +85°C.
Data Sheet, Rev A, 08/2008
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At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Jumpers provide for exercising the user-selectable features of the AD8335, such as the preamp and VGAs and the optional high and low gain ranges. Test pins are provided for power and gain voltage connections and for probes used to observe waveforms at the input and outputs. Provisions are also made for driving the gain controls dynamically.
See the AD8335 data sheet for measurement setup, board layout and further details.
Product Selection Guide
Variable Gain Amplifier Selection Table
How Ultrasound System Considerations Influence Front-End Component Choice
by Eberhard Brunner, Analog Devices, Inc.
(Analog Dialogue Vol. 36, May-July 2002)
Temperature monitor measures three thermal zones
by Susan Pratt, Analog Devices, Inc. (EDN, 12/11/03)