Linear Technology 1Msps, 20-Bit Precision ADC
The LTC2378-20 is a 20-Bit No-Latency Serial SAR ADC with 1Msps throughput & 0.5ppm INL
Just when you thought SAR ADCs could not get wider dynamic range at reasonable speeds, Linear Technology Corporation introduced the LTC2378-20, a 20-bit 1Msps no latency successive approximation register (SAR) analog-to-digital converter (ADC) with low 0.5ppm (typ) and 2ppm (max) Integral Non-Linearity (INL) error.
Many precision industrial systems require high-resolution analog to digital converters (ADCs) to digitize real-world analog signals. In order to achieve parts per million (ppm)-level resolution and accuracy, many precision industrial systems are digitally calibrated to null out any system-level offset and gain errors. As a result, system accuracy is often limited by errors that cannot be suppressed by infrequent calibration, for example drift over wide temperature excursions.
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 proprietary architecture leads to a stable 2ppm (max) INL and -114dB THD (max) over the device’s entire operating range of -40°C to 85°C.
The ADC achieves what Linear Technology claims is the industry’s highest signal-to-noise ratio (SNR) of 104dB for a 1Msps 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.
The IC is in a pin- and software-compatible family of 20/18/16-bit SAR ADCs with speeds ranging from 250ksps up to 2Msps with serial SPI interfaces. The 20-bit 250ksps (LTC2376-20) and 500ksps (LTC2377-20) versions will be released later in May.
The family operates from a 2.5V supply, with a ±5V fully differential input range using an external 5V reference. At 1Msps, the device achieves low power dissipation of 21mW, which scales linearly with sample rate. A shutdown mode further reduces power dissipation to 2.5μW when idle.
The ADC 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 beauty of Digital Gain Compression:
LTC2378-20 input accepts signal with 90% compression with respect to reference and the ADC digitizes the range using all codes
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, the LTC6362, a fully differential driver operating from a single 5V supply (1mA) is a good choice. This combination 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 an MSOP-16 and 4mm x 3mm DFN-16 packages, priced starting at $29.50, $25.50 and $18.17 each, respectively, in 1,000 piece quantities. For more information, visit www.linear.com/product/LTC2378-20.