‘Most accurate’ 20bit SAR ADC ever




Description

The LTC®2378-20 is a low noise, low power, high speed 20-bit successive approximation register (SAR) ADC. Operating from a 2.5V supply, the LTC2378-20 has a ±VREF fully differential input range with VREF ranging from 2.5V to 5.1V. The LTC2378-20 consumes only 21mW and achieves ±2ppm INL maximum, no missing codes at 20 bits with 104dB SNR.

The LTC2378-20 has a high speed SPI-compatible serial interface that supports 1.8V, 2.5V, 3.3V and 5V logic while also featuring a daisy-chain mode. The fast 1Msps throughput with no cycle latency makes the LTC2378-20 ideally suited for a wide variety of high speed applications. An internal oscillator sets the conversion time, easing external timing considerations. The LTC2378-20 automatically powers down between conversions, leading to reduced power dissipation that scales with the sampling rate.

The LTC2378-20 features a unique digital gain compression (DGC) function, which eliminates the driver amplifier’s negative supply while preserving the full resolution of the ADC. When enabled, the ADC performs a digital scaling function that maps zero-scale code from 0V to 0.1 • VREF and full-scale code from VREF to 0.9 • VREF. For a typical reference voltage of 5V, the full-scale input range is now 0.5V to 4.5V, which provides adequate headroom for powering the driving amplifier from a single 5.5V supply.

Features

  • 1Msps Throughput Rate
  • ±0.5ppm INL (Typ)
  • Guaranteed 20-Bit No Missing Codes
  • Low Power: 21mW at 1Msps, 21μW at 1ksps
  • 104dB SNR (Typ) at fIN = 2kHz
  • –125dB THD (Typ) at fIN = 2kHz
  • Digital Gain Compression (DGC)
  • Guaranteed Operation to 85°C
  • 2.5V Supply
  • Fully Differential Input Range ±VREF
  • VREF Input Range from 2.5V to 5.1V
  • No Pipeline Delay, No Cycle Latency
  • 1.8V to 5V I/O Voltages
  • SPI-Compatible Serial I/O with Daisy-Chain Mode
  • Internal Conversion Clock
  • 16-Lead MSOP and 4mm × 3mm DFN Packages
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'Most accurate' 20bit SAR ADC ever




Linear Technology has announced what it claims is the most accurate ADC, with INL errors of 2ppm maximum over temperature.

LTC2378-20 is the first 20bit SAR ADC on the market offering ±0.5ppm typical integral nonlinearity [INL] error with a guaranteed specification of 2ppm maximum over temperature, making it the most accurate ADC in the industry. With 104dB SNR it has the industry’s highest SNR performance for any 1Msample/s no-latency ADC,” claimed the firm.

Offset error is specified at 13ppm maximum with 0.007ppm/°C drift, and the gain error is 10ppm with 0.05ppm/°C drift.

Inside, the critical blocks are a capacitor-based DAC, a low-noise comparator, and a successive-approximation register.

“It achieves its INL performance by implementing a proprietary architecture that makes the INL independent of DAC capacitor mismatch, thus making it robust to temperature variations and package stress,” said the firm. And, due to the comparator design, 104dB signal-to-noise ratio (SNR) is achieved with 21mW power consumption at 1Msample/s without any cycle latency: “consumption is proportional to the sampling rate, so they consume only microwatts when operated at 1ksample/s”.

The chip is the flagship of a range of pin and software-compatible SPI-interface 20/18/16bit SAR ADCs with speeds from 250k to 2Msample/s.

All operate from a 2.5V supply, with a ±5V differential input range using an external 5V reference.

“The family offers a unique digital gain compression 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”, said the firm. There is also a 2.5μW shut down mode.

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For more read: ‘Most accurate’ 20bit SAR ADC ever




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