Current-to-bits converter fast enough for optical reflectometry

In a 12 x 6mm BGA package, the IC is actually a hybrid module combining transimpedance amplifier, analogue low-pass filter and 14bit 125Msample/s ADC converter.

The output is through two serial LVDS (low-voltage differential signalling) lanes at up to 1Gbit/s/lane. The data clock output operates at up to 500MHz and supports double data-rate (DDR).

To maximise useful dynamic range, the amplifier has three gain settings (2kΩ – 800μA full scale, 20kΩ or 200kΩ), and the filter can limit bandwidth to 100MHz to minimise broadband noise and act as an anti-aliasing filter, or can be set to 1MHz to reduce noise with lower bandwidth signals, or input pulses of 20μs or wider.

Maximum input is 40mA, and input-referred noise is 16pArms (200kΩ amplifier, 65,536x averaging 1MHz filter).

Operation is from 3.3V and an internal 1.8V LDO is provided for the ADC – all supply decoupling is integrated. Power is 546mW including LDO and operation is over -40 to +85°C.

“The device is supported by the EVAL-ADA4355 evaluation system,” according to Anglia, which is stocking the device and the kit. It “couples the Analog ADA4355 evaluation board to a Xilinx KC705 FPGA evaluation platform and provides ample memory, GPIOs and processing power to perform all control and data manipulation functions. All evaluation system control and data processing is accomplished via a MATLAB-based graphical user interface”.

As well as time-of-flight measurement, for example in optical time-domain reflectometry, use is foreseen amplifying small currents in chemical analysers and mass spectroscopy.

Anglia has a ADA4355 product page here