読み物

Maithil Pachchigar About The Author
Maithil Pachchigar ,
アプリケーション・エンジニア

Selecting an ADC driver to achieve optimized signal chain performance

Precision high-speed data-acquisition systems used in multichannel applications require state-of-the-art performance. This analog tip covers the specifications that are critical to consider when selecting an ADC driver to optimize signal chain performance. 

The figure shows a high-precision, low-noise, 18-bit data-acquisition signal chain that features ±0.8-LSB integral nonlinearity (INL), ±0.5-LSB differential nonlinearity (DNL), and 99-dB signal-to-noise ratio (SNR). The AD7960 18-bit, 5-MSPS PulSAR differential ADC uses a capacitive digital-to-analog converter (CAPDAC) to provide unprecedented noise and linearity without latency or pipeline delay. It provides the wide bandwidth, high accuracy (100 dB DR), and fast sampling (200 ns) required for multiplexed applications, while significantly reducing power dissipation and cost in multichannel applications.


Precision, fast-settling signal chain using AD7960, ADA4899, AD8031, and ADR4550

ADC Driver
The acquisition time of the ADC determines the settling time requirements for the ADC driver. The table shows some specifications that must be considered when selecting an ADC driver. As always, the signal chain performance should be verified on the bench to ensure that the desired performance is achievable.

AD7960 ADC Driver Selection Benchmark
ADC Driver Specifications General Formula Minimum Requirements
Bandwidth
(f-3db_amp)
Bandwidth formula
40MHz
Slew Rate Slew rate formula
100 V/µs
Settling Time From data sheet
100 ns
SNR
SNR formula
105.5 dB
Notes: N = 18, tacq = 100 ns, Vrms_in2 = 52/2 = 12.5 V2, en_amp = 2 nV/√Hz,  f–3dB_ADC = 28 MHz.

The op amp data sheet usually specifies the settling time as the combined time for linear settling and slewing; the formulas given are first-order approximations assuming 50% for linear settling and 50% for slewing (multiplexed application) using a 5-V single-ended input. 

The ADA4899-1 rail-to-rail amplifier features 600-MHz bandwidth, –117-dBc distortion @ 1 MHz, and 1-nV/√Hz noise. It settles to 0.1% within 50 ns when configured as a unity-gain buffer driving the inputs of the AD7960 with a 5-V differential signal.

Maithil Pachchigar はアナログ・デバイセズの計装/高精度テクノロジー部門のアプリケーション・エンジニアです。2010 年にアナログ・デバイセズに入社して以来、高精度 ADC の製品ポートフォリオを担当し、産業分野、計測分野、医療分野、エネルギー分野のお客様を支援しています。2005 年から半導体業界に携わっており、数件の技術資料を発表しています。2006年にサンノゼ州立大学で電気電子工学の修士号を取得し、2010 年にシリコン・バレー大学で経営学の修士号を取得しています。