Optimizing Digital noise issue with XDAQ with X6R128 or Intan RHD2164

Optimizing Digital noise issue with XDAQ with X6R128 or Intan RHD2164

Issue Description

Some XDAQ users have reported noise affecting blocks of 32 channels, particularly when using longer cables with KonteX's X6R128 or Intan RHD2164 chip/probes. This issue is likely due to nanosecond-scale timing inconsistencies in signal transmission between the XDAQ and the headstage. These inconsistencies can result from a combination of factors, including cabling, adapters, and parasitic capacitance in the I/O connections. The problem tends to be more pronounced with the X6R128 and RHD2164 chips, which rely on the double-data-rate (DDR) SPI protocol.  This issue is caused by digital interference, which should not impact analog performance once the correct cable delay is selected.

Solution

1. Use Firmware version 78a5a821 or later

Firmware version 78a5a821 or later includes additional optimization on the latency compensation.  

XDAQRHD.bit
Version: 78a5a821. 
MD5: 197248c4efc6be239cfb9d5a2997ac02).
Release note (coming soon).

The updated FPGA firmware is also included in the XDAQ-RHX Version 1.1.5 or later.  Users can also download (XDAQRHD_78a5a821.zip) and replace the bitstream (may need to rename file to match software) used in the software.

2. Cable Delay Adjustment

Automatic Delay Calibration

Each time the XDAQ compatible software is opened or the Rescan Ports button is clicked, the software performs an analysis to determine the optimal delay settings for each headstage port. However, this delay-setting algorithm may occasionally fail.

Manual Delay Adjustment

If you encounter noisy signals with large discontinuities on a particular headstage port, you can manually override the delay-setting algorithm:
  1. Apply Manual Delay for the affected port.
  2. Adjust the delay setting incrementally, increasing or decreasing by one step at a time.

Verifying Adjustments

To confirm a successful adjustment, in vitro test can be done using one of the following methods:
  1. Grounded Saline Bath: Measure the signal response in a saline bath with the probes grounded.
  2. Signal Generator: Use a signal generator, such as the Brainwave simulator, to verify signal integrity.
By manually fine-tuning the delay settings, you can mitigate noise and improve the signal quality in XDAQ systems using X-headstage or other Intan RHD2000 headstages.

3. Example

Configuration

X6R128 attached directly to the Brainwave Simulator.  Output is set to ground. XDAQ-RHX 1.1.5 is used.

1. Noisy waveform observed while inputs are grounded


2. Adjust the delay ( adjusting from 6 to 5 in this case )


3. Restart streaming and observe stable waveform




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