FTMW Digitizer

Overview

The FTMW Digitizer is the fast digitizer used to record FIDs during a CP-FTMW experiment. At its simplest, on each trigger event the digitizer records a fixed number of points at the configured sample rate and sends the raw samples to Blackchirp for averaging. Some devices support fast retriggering (e.g., Tektronix’s “FastFrame” mode), which lets a series of frames be acquired in a single shot. For pulsed gas sources this allows each gas pulse to be probed by a series of chirps, with the resulting frames transmitted individually.

Many digitizers also support internal averaging (sometimes called block averaging), where some number of records are co-averaged on the device before transfer. On some scopes block averaging produces a single averaged frame; others can co-average multiple records in parallel and transfer a record that still contains several (averaged) frames.

Regardless of how many analog channels the digitizer has, Blackchirp records data from a single input channel.

To keep up with high shot rates, Blackchirp owns a small fixed-size buffer between the digitizer thread and the acquisition thread. If processing falls behind, the digitizer automatically accumulates shots locally so that no triggers are lost; the accumulated data is handed off as soon as the buffer drains. This is transparent to the user, but it means that brief stalls in the GUI or storage path do not corrupt the shot count.

Note

Some errors on Keysight and Tektronix scopes can leave the instrument unresponsive. For Keysight scopes, closing and reopening the scope software clears the condition. For Tektronix scopes, a full instrument restart is usually required.

Settings

Most digitizer settings are exposed in the hardware dialog with inline labels and tooltips, so they do not need to be re-documented here. A few behaviors are worth highlighting:

  • Capability flags (canBlockAverage, canMultiRecord, canBlockAndMultiRecord, hasAuxTriggerChannel) describe what the device supports. Drivers set these to match the hardware; do not enable a capability the device cannot actually provide.

  • Memory-derived limits (maxRecordLength, maxRecords, maxAverages) reflect device memory. Enabling multi-record mode divides the available memory among records, and on some devices enabling block averaging further reduces the usable record length.

  • Sample rates are presented as a fixed menu of supported values rather than a free-form numeric entry, because most scopes only accept a discrete set.

  • bandwidthMHz is informational only; it does not change the configuration sent to the device.

Transfer rate is often the practical bottleneck. Two recommendations that still apply:

  • Prefer a link-local Ethernet connection of at least 1 Gbps to network-attached scopes; lower bandwidth quickly becomes the limit for long records or fast retriggering.

  • Where the digitizer supports it, enable block averaging to push co-averaging onto the device. The record sent to Blackchirp is then the sum of many shots, which dramatically reduces network traffic and host-side processing per FID.

Drivers

Virtual

The virtual driver synthesizes a fresh FID on every shot by summing 10–100 sinusoidal components at randomly chosen frequencies, amplitudes, and phases, then adds Gaussian noise at the byte width configured for the run. It honors the current vertical scale, sample rate, and byte order, so changes made in the dialog take effect immediately. The driver is intended for development and for installs that only view archived data; it should not be enabled on a real acquisition machine.

Tektronix DSA71604C

A 4-channel, 100 GSa/s oscilloscope with 16 GHz analog bandwidth. It supports FastFrame acquisition, so a variable number of waveforms can be captured with a low retrigger interval (about 4 μs); the frame count is bounded by scope memory. The scope can co-average frames and send only the average; Blackchirp uses this mode when block averaging is enabled. Communication is over TCP, and a link-local connection of at least 1 Gbps is recommended. In practice the scope’s internal processing, not network bandwidth, often sets the throughput limit.

Tektronix MSO72004C

Functionally identical to the DSA71604C, but with 20 GHz analog bandwidth.

Keysight DSOV204A

The DSOV204A is an 80 GSa/s oscilloscope with up to 20 GHz of bandwidth. Communication is over a TCP socket on port 5025, requiring a static IP address configured in the Windows OS running on the scope. The scope can be triggered on any of its four analog channels, but triggering on the AUX channel is recommended.

Keysight DSOX92004A

The DSOX92004A is an 80 GSa/s oscilloscope with 20 GHz of bandwidth, upgradable to 33 GHz. Communication is over a TCP socket on port 5025, requiring a static IP address configured in the Windows OS running on the scope. Treat this driver as untested.

Tektronix MSO64B

A 4-channel scope with 2.5 GHz bandwidth, suitable for segmented LO scanning. Tektronix’s FastFrame backend on this model breaks the CURVESTREAM mode that Blackchirp relies on for fast real-time data transfer, so the data transfer rate of this scope is severely limited.

Spectrum Instrumentation M4i2220x8

A high-speed digitizer with a 2.5 GSa/s sampling rate and 1.25 GHz analog bandwidth, suitable for segmented LO scanning. The driver requires the device to have the block-averaging firmware module enabled; with that module, sustained acquisition rates of 50,000 FIDs/s have been achieved.

This driver requires the Spectrum Instrumentation spcm library to be installed on the host. See Library Status for installation details and to confirm that Blackchirp has located the library.

Tektronix DPO71254B

The DPO71254B is a 50 GSa/s oscilloscope with up to 12.5 GHz of bandwidth. Communication is over a TCP socket on port 4000, the default for TekVisa, requiring a static IP address configured in the Windows OS running on the scope. The scope can be triggered on any of its four analog channels, but triggering on the AUX channel is recommended. Treat this driver as experimental.