1 Features
• Single-chip solution to directly measure 256 lowlevel
currents simultaneously
• Adjustable full-scale charge range up to 320 pC
• Input current: 1 μA (maximum)
• Adjustable speed with integration times as low as
50 μs (20 KSPS per channel)
• Resolution: 24 bit
• Low power dissipation: 1.2 mW/channel
• Integral non-linearity: ±0.025% of reading ±1 ppm
of full scale range (all channels active)
• Low noise: 0.26 fCrms at 320 pC FSR with 20 pF
sensor capacitance
• No charge loss
• On-chip temperature sensor
• Serial LVDS output interface
• Single 1.85-V supply
• In-package bypass capacitors and reference buffer
to reduce PCB area and design complexity

2 Applications
• CT Scanner data acquisition system
• Photodiode sensors
• X-ray detection systems
• Optical fiber power monitoring
• Muti-channel current, voltage instrumentation

3 Description
The DDC3256 is a 24-bit, 256-channel, current-input
analog-to-digital (A/D) converter. It combines both,
current-to-voltage conversion by current integration,
and A/D conversion.
Up to 256 individual low-level current output devices,
such as photodiodes, can be directly connected to its
inputs and digitized in parallel (simultaneously).
For each of the 256 inputs, the device has one
low noise and low power integrator designed to
capture all the charge from the sensor. The integration
time is adjustable from 50 μs to 1.6 ms, allowing
currents in the order of fA to μA to be continuously
measured with outstanding precision. The outputs of
the integrators are digitized by on-chip low power
ADCs and the converted digital codes are transmitted
over a single LVDS pair designed to minimize noise
coupling in environments with high channel count.
The DDC3256 operates from single 1.85-V supply.
The device is specified from 0°C to 70°C operating
temperature and available in a 13.2 × 17.2 mm2 336-
ball 0.8 mm-pitch BGA. The on-chip reference buffer
and bypass capacitors (on the BGA) help minimize
the external component requirements and further
reduce board space.