WFD20 – 20 bit / 2 MS/s Waveform Digitizer

DC to 20kHz spectrum, 1KHz carrier, 800kHz filter-on

The WFD20 is a 20 bit Waveform Digitizer for medium-speed / high resolution waveform capturing and analyzing. The module combines an excellent dynamic performance with a very high DC accuracy. The module features a fully differential input path to reduce common-mode level disturbances. If the internal DC-offset voltage source is used, the negative input can still be used as a GND Sense input, so the DC performance won’t be compromised due to ground currents. The module has 8 input ranges from 0.544 Vpp to 8.16 Vpp, which allows easy adaptation to a wide range of Unit Under Test output voltages.

A filter-bank with 3 Low Pass filters (40 kHz, 250 kHz and 800 kHz) provide excellent signal conditioning to obtain the best result in dynamic performance: low noise and anti-aliasing. The special combination of four 18 bit ADCs to a 20 bit converter gives an excellent SNR and linearity and a resolution down to 0.52 µV. With 4M-word (12M-byte) of memory a large number of samples can be captured. All these features ensure a very accurate result when performing analog measurements. The unit is very suitable for testing DAC linearity and dynamic performance.

Block Diagram

WFD20 – 20 bit / 2 MS/s Waveform Digitizer

Key Features

  • 2 MHz max sample speed
  • 20 bit resolution
  • Fully differential input
  • 8 input ranges
  • Selectable filters to reduce out-of-band noise
  • -119 dB THD typical (f-in = 1 kHz)
  • 96 dB SNR typical (DC - 800 kHz)
  • Programmable DC-offset voltage
  • For ATX series hardware platform

Technical Specifications

General

Resolution 20 bit
Sample rate 1.5 kHz - 2 MHz in warp mode, 0 - 1.5 MHz in normal mode
Pattern depth 4M words

Input characteristics

Input impedance 100 MOhm
Input ranges 0.544 Vpp, 0.816 Vpp, 1.36 Vpp, 2.04 Vpp, 2.72 Vpp, 4.08 Vpp, 5.44 Vpp, 8.16 Vpp
Input filters Bypass, 40 kHz (4-pole Butterw.), 250 kHz (5-pole Butterworth), 800 kHz (7-pole elliptic)
Bandwidth -3 dB (typical) 2 MHz (8.16 Vpp range)
0.1 dB flatness (typical) 400 kHz (8.16 Vpp range)
Input configuration Differential / Single Ended (-Input to Gnd, Gnd-sense or DC offset)
Input Common mode range +/- 10 V

Accuracy (DC-offset off, filter bypass)

Absolute accuracy ±(40 µV + 10 ppm of range)
Non Linearity error ±8 ppm of range (3 ppm typical)
Temperature drift (typical) ±(1 ppm of range + 2 ppm of reading)/ºC

DC-offset source

Resolution 19 bit (20 µV)
Voltage range -5 V to +5 V
DC-offset accuracy ±(50 µV + 12 ppm of value)
Non Linearity ±10 ppm of range

Dynamic characteristics

(conditions: 1.67 MS/s, 800 kHz filter on)

SNR (5 Vpp, 1 kHz input) 93 dB
SNR (5 Vpp, 10 kHz input) 92 dB
SNR (5 Vpp, 100 kHz input) 91 dB
SNR (1 kHz input, A-weighted) 105 dB (BW 20 Hz - 20 kHz)
THD (2 Vpp, 1 kHz input) -110 dB
THD (2 Vpp, 10 kHz input) -106 dB
THD (2 Vpp, 100 kHz input) -92 dB
SFDR (2 Vpp, 1 kHz input) 108 dB

Clock & Trigger inputs

Input impedance > 1 MOhm
Threshold level 3.3 V CMOS/TTL (5 V tolerant)