Hardware Operation and Settings on Swabian Instruments

Recommended SMA Cables for Time Taggers

Thu, 12 Dec 2024 00:00:00 +0000

SMA cables are the cable of choice when connecting a Time Tagger with a device.

As a reference, to test our devices internally, we mainly use two types of cables. One type for standard usage (see under this link), and one used to achieve better signal-to-noise ratios (see under this link).

More specifically, there are many parameters to consider when selecting an SMA cable:

Length. Ideally, the Time Tagger has to be placed close to the experimental setup, and USB extenders should be used to cover longer distances. When this solution is not possible, we would suggest keeping the length of the SMA cable below five meters. Our devices can work with longer cables, but the signal can degrade, affecting the overall jitter.

Suitable Pulse Shapes for Time Tagger Measurements

Thu, 12 Dec 2024 00:00:00 +0000

The Time Tagger detects electrical signals that rise or fall across a user-defined trigger level. Such events are acquired with a resolution of 1 ps and a specific time jitter for each model. This is independent of the input signal’s shape (square, triangle, sine, or any arbitrary shape), as long as the signal’s slew rate is sufficiently high to be detected by the Time Tagger within the specified timing accuracy.

Detecting Negative Signals with Time Tagger 20

Thu, 12 Dec 2024 00:00:00 +0000

The Time Tagger 20 can accept only positive signals and requires a pulse inverter to be used with negative polarity signals. A pulse inverter is usually a simple passive component that inverts pulse polarity. Passive inverters use a type of transformer, transfer only alternating signals, and work in a specific frequency range. They may perform poorly when used outside their design frequency range, leading to signal distortion and incomplete inversion.

Setting the Appropriate Trigger Level

Thu, 12 Dec 2024 00:00:00 +0000

Choosing the appropriate trigger level depends on the characteristics of your signal. Our general recommendation is to set the trigger level to half of the signal’s maximum amplitude, as this typically corresponds to the steepest part of the signal.

Additionally, whenever possible, select the sharpest edge of the signal, either the rising edge (positive channel number) or the falling edge (negative channel number). A steep signal edge results in better time definition and is less sensitive to noise compared to slower transitions, which are affected by noise for a longer duration.

Maximum Input Voltage Amplitude

Thu, 12 Dec 2024 00:00:00 +0000

For each model, we specify an input signal range:

Time Tagger 20: 0 to 3 V
Time Tagger Ultra: -3 to 3 V
Time Tagger X: -1.5 to 1.5 V

Amplitudes slightly beyond the limits can still be applied without causing damage, but specified performances are not guaranteed. Please have a look at our brochure.

If your signal has an amplitude outside the accepted range, we recommend using SMA attenuators.

Minimum Pulse Amplitude and Duration Requirements

Thu, 12 Dec 2024 00:00:00 +0000

For all Time Tagger models, we specify a minimum input signal amplitude of 100 mV. The minimum pulse duration requirements are as follows:

Time Tagger X: 350 ps
Time Tagger Ultra: 500 ps
Time Tagger 20: 1 ns

While these values provide a useful baseline, it is important to consider a few additional factors, as reducing specifications to single numbers does not tell the full story:

When the trigger level is properly selected and the system is correctly set up, these specifications guarantee a 100% count rate and a time jitter below the specified value for each model.
Shorter or smaller pulses can still be detected, but this may result in:
- A count rate below 100% (missed events).
- Time jitter exceeding the specified values.
These specifications for amplitude and duration are interdependent:
- Shorter pulses might still work if their amplitude is higher than 100 mV, while meeting jitter specifications and avoiding missed events.
- Conversely, longer pulses with an amplitude slightly below 100 mV may also function correctly.

By carefully tuning your setup, you can optimize the performance of your Time Tagger, even when operating near the specified limits.

Compensating for Channel Delays

Thu, 12 Dec 2024 00:00:00 +0000

The overall delay between channels results from delays accumulated at different stages.

We refer to the external delay as the delay accumulated before the signals are fed into the TimeTagger. This delay between the signals arises from experimental conditions, such as different optical paths/different cables length/inherent delays in the detectors. Next, there is the hardware or internal delay due to the different paths of the different channels through the FPGA, where the time to digital conversion occurs. In principle we should distinguish between input time stamps and TDC time stamps, because of the different hardware delays accumulated between the propagating signals at the hardware level. Nevertheless, the Time Tagger is calibrated to compensate for this delay, and no distinction is needed.

Detecting Falling Edges of Pulses

Thu, 12 Dec 2024 00:00:00 +0000

On the software level, the rising and falling edges are independent channels. In the Graphical User Interfaces, Time Tagger Lab, the rising and falling edges are marked explicitly with a pictogram. In the software libraries, the number of a falling edge channel is a negative number of the physical input. For example, the rising and falling edges of the physical input 2 correspond to the software channels 2 and -2, respectively. You can also use the method getInvertedChannel() to find the inverted channel number for your specific hardware revision.