Linearization of ADCs - ADL

Digital post‑linearization increases the effective resolution of analog‑to‑digital conversions. The linearization technology developed by SP Devices suppresses low order non‑linearities of high‑performance ADCs and non‑linearities caused by pre‑ADC analog components (such as amplifiers, filters and buffers).

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The transfer function of ADCs
The SP Devices linearization technology increases the useful dynamic range of A/D solutions. An ADC can be viewed as a transfer function from the analog to digital domain. An ideal ADC has a completely linear transfer function.

The transfer function of ADCs

All ADCs are non-linear
However, the transfer functions of all real ADCs suffer from non‑linearities. These non‑linearities limit the dynamic range of the ADC and often limit the usefulness of many applications.

Non‑linearities

The ADL technology
ADL is a digital block for the post‑processing of the output from ADCs that enhances the linearity of the ADC. ADL improves the dynamic range in most applications by a factor of at least two.

ADL compensates

  • Static non-linearities
  • Frequency dependent non-linearities

ADL features

  • Black-box model which captures frequency dependent non-linear behavior
  • Suppresses low-order non-linear distortion
  • SFDR for higher Nyquist zone improved to the same levels as lower Nyquist zone
ADL - Linearization for ADCs


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ADL improvement results

The plots below show the result of applying ADL to the output of high-speed 16-bit ADCs mounted on reference boards available from each of the ADC manufacturers. The boards were operated at a sampling rate of 130 MSPS, and the plots show two-tone tests in the 5th Nyquist zone before (left) and after (right) being corrected by ADL. In this Nyquist zone, distortion is dominated by low order harmonic distortion, (HD2 and HD3). The plots show that regardless of the ADC model, the 2:nd and 3:rd order distortion spurs are attenuated to a level close to -100 dBFS. This means that the usable bandwidth is extended up to the 5th Nyquist Zone.

Analog Devices AD9461

Analog Devices AD9461


National Semiconductor ADC16V130

National Semiconductor ADC16V130

Texas Instruments ADS5483

Texas Instruments ADS5483

Linear Technology LTC2209

Linear Technology LTC2209

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