Power Electronics
No Latency 20-Bit SAR ADC

No Latency 20-Bit SAR ADC

The LTC2378-20 from Linear Technology Corporation is a 20-bit 1Msps no latency successive approximation register (SAR) analog-to-digital converter (ADC) with exceptionally low 0.5ppm (typ) and 2ppm (max) Integral Non-Linearity (INL) error. INL is a key specification in precision applications, such as seismic monitoring and semiconductor fabrication, indicating how much the ADC transfer function deviates from its ideal. Since linearity effectively cannot be calibrated at the system level, the ADC's INL specification often sets the overall system accuracy. The best-in-class 0.5 ppm INL of the LTC2378-20 enables a new generation of precision systems with true 20-bit accuracy. Proprietary architecture leads to an extremely stable 2ppm (max) INL and -114 dB THD (max) over the device's entire operating range of -40 °C to 85 °C.

The LTC2378-20 achieves the industry's highest signal-to-noise ratio (SNR) of 104 dB for a 1 Msps no latency ADC. The wide dynamic range and true 20-bit resolution reduce or eliminate the need for additional gain in the signal chain, thereby improving total system accuracy and noise. Fast 1Msps throughput with no latency enables the use of multiplexers to replace costly, independent ADCs with slower throughputs, thus reducing system cost and complexity.

The LTC2378-20 is the leadership product in a pin- and software-compatible family of 20/18/16-bit SAR ADCs with speeds ranging from 250 ksps up to 2Msps with serial SPI interfaces. The 20-bit 250 ksps (LTC2376-20) and 500ksps (LTC2377-20) versions will be released in May. The family operates from a 2.5 V supply, with a ±5 V fully differential input range using an external 5 V reference. At 1 Msps, the device achieves low power dissipation of 21 mW, which scales linearly with sample rate. A shutdown mode further reduces power dissipation to 2.5 µW when idle. The LTC2378-20 family offers a unique digital gain compression (DGC) feature, eliminating the need for a negative ADC driver supply and preserving the full resolution of the ADC, to achieve lower total power consumption of the signal chain with only a small reduction in SNR performance.

The DC1925A evaluation kit demonstrates the 0.5ppm INL and 104dB SNR performance of the LTC2378-20. The board features the flexible LT6203 ADC driver for interfacing differential or single-ended input signals and the 5V LTC6655-5 precision, low noise, low power reference. For a truly low power signal chain solution using the digital gain compression feature, we recommend the LTC6362 fully differential driver operating from a single 5 V supply (1 mA), which achieves up to 100dB SNR performance when combined with the LTC2378-20 and the 4.096V LTC6655-4.096 reference.

The LTC2378-20, LTC2377-20 and the LTC2376-20 are available in small MSOP-16 and 4 mm x 3 mm DFN-16 packages, priced starting at $29.50, $25.50 and $18.17 each, respectively, in 1,000 piece quantities.  

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