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Digital Gain Compression (DGC) for SAR ADCs

The LTC2378-20 offers a digital gain compression (DGC) feature which defines the full-scale input swing to be between 10% and 90% of the ±VREF analog input range. This feature allows the SAR ADC driver to be powered off of a single positive supply since each input swings between 0.5V and 4.5V as shown in the figure below.

Digital Gain Compression Graphic

Needing only one positive supply to power the SAR ADC driver results in additional power savings for the entire system. With DGC enabled, the LTC2378-20 can be driven by the low power LTC6362 differential driver which is powered from a single 5V supply. To enable digital gain compression, bring the REF/DGC pin low. Figure 1 shows how to configure the LTC6362 to accept a ±3.28V true bipolar single-ended input signal and level shift the signal to the reduced input range of the LTC2378-20 when digital gain compression is enabled. When paired with the LTC6655-4.096 for the reference, the entire signal chain solution can be powered from a single 5V supply, minimizing power consumption and reducing complexity.

LTC2378 DGC CircuitFigure 1: LTC6362 Configured for a ±3.28V Input; LTC2378 with Signle Supply and DGC

 

As shown in the following FFT plot, the single 5V supply solution can achieve up to 100dB of SNR, which though not as good as the 104dB for the dual supply FFT plot with no digital gain compression, provides a substantial power savings while still maintaining very good performance.

LTC2378 FFT DGC and No DGC

Linear Technology has several SAR ADCs that feature digital gain compression. These devices reduce your power budget and simplify your design while still providing very good performance