The LTC2378-20 provides a digital gain compression (DGC) function that defines the full-scale input swing as between 10% and 90% of the ±VREF analog input range. This feature allows a single positive power supply to power the SAR ADC driver because each input swings between 0.5V and 4.5V, as shown in the figure below.
Since only a positive power supply is needed to power the SAR ADC driver, additional power savings can be achieved for the entire system. When the DGC function is enabled, the LTC2378-20 can be driven by a low-power LTC6362 differential driver powered by a single 5V power supply. To enable digital gain compression, pull the REF/DGC pin to a low level. Figure 1 shows how to configure the LTC6362 to accept a ±3.28V true bipolar single-ended input signal and shift the signal level to the reduced input range of the LTC2378-20 when the digital gain compression function is enabled. When paired with LTC6655-4.096 for reference, the entire signal chain solution can be powered by a single 5V power supply, thereby minimizing power consumption and reducing complexity.
Figure 1: LTC6362 is configured for a ±3.28V input; LTC2378 with single power supply and DGC
As shown in the FFT graph below, this single 5V power supply solution can achieve SNR as high as 100dB. Although not as good as the 104dB given by the dual power supply FFT graph without digital gain compression, it provides substantial savings. While still maintaining very good performance.
Linear Technology has a variety of SAR ADCs with digital gain compression. These devices not only reduce the power budget and simplify the design, but also provide very good performance.
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