Hardware

Input channels

The Time Tagger has 8 or 18 inputs (SMA-connectors). The electrical characteristics are tabulated below. Each input can detect both, rising and falling edges of an input pulse, and each input has two channels associated with it. Rising edges correspond to channel numbers 1 to 18 (Time Tagger 20: 1 to 8) and falling edges correspond to respective channel numbers -1 to -18 (Time Tagger 20: -1 to -8). Thereby, you can treat rising and falling edges in a fully equivalent fashion.

Electrical characteristics

Property	Time Tagger 20	Time Tagger Ultra	Time Tagger X
Termination	50 Ohm	50 Ohm	50 Ohm / High-Z
Input voltage range (recommended)	0.0 to 3.0 V	-3.0 to 3.0 V	-1.5 to 1.5 V
Maximum input (no damage)	-0.3 to 5.0 V	-5.0 to 5.0 V	-3.0 to 3.0 V
Trigger level range	0.0 to 2.5 V	-2.5 to 2.5 V	-1 to 1 V
Minimum signal level	100 mV	100 mV	100 mV
Minimum pulse width	1.0 ns	0.5 ns	350 ps

Configurable input termination - Time Tagger X only

The input termination of the Time Tagger X is configurable during runtime to either 50 Ohm or High-Z (see TimeTagger.setInputImpedanceHigh()). Usually 50 Ohm should be chosen to accomplish proper HF termination, but High-Z is useful in certain use cases with small amplitudes and weak output drivers.

Caution

When the Time Tagger X is unpowered or not configured (before createTimeTagger() has been called), the input termination is High-Z. This is to protect the Time Tagger’s input stage from potentially damaging operating conditions (e.g. signals into an unpowered input stage). Since software version 2.17.0, the termination does not switch switch to 50 Ohm upon initialization anymore. However, the channel will switch to 50 Ohm by default as soon as it is registered. To prohibit this switching behavior, set the impedance explicitly to High-Z by TimeTagger.setInputImpedanceHigh() before the first usage of the respective input, e.g. in a measurement.

One of the following measures can be taken when connecting signal sources to the Time Tagger X which are sensitive to operation without termination:

The signal source is only operated after the Time Tagger X is powered and configured properly. The Time Tagger’s input termination is set to 50 Ohm.
An external 50 Ohm termination is connected between SMA cable and the Time Tagger’s input port. The Time Tagger’s input termination is set to High-Z.
An HF circulator or isolator is connected to the output of the signal source to prevent any potentially damaging reflections from getting into the output.

High Resolution Mode

The Time Tagger Ultra Performance and the Time Tagger X can operate in different High Resolution (HighRes) modes. An increased resolution is achieved by directing the signal from a single input to multiple time-to-digital converters (TDCs). Depending on the mode, 2, 4, or 8 TDCs are used per input. By averaging the results, a single timestamp with lower jitter is generated. On the other hand, this process reduces the number of usable signal inputs.

The tables show the usable inputs for the different modes. Channels available with the minimal four-channel license are shown without parenthesis. When additional channels are added, the priority will be given to the HighRes ones.

Time Tagger Ultra Performance
Mode	HighRes channels	Standard channels
Standard		1 - 4, (5 - 18)
HighResA	1, 3, 5, 7, (10, 12, 14, 16)	(9, 18)
HighResB	1, 5, 10, 14	(9, 18)
HighResC	5, 14	9, 18

Time Tagger X
Mode	HighRes channels	Standard channels
Standard		1 - 4, (5 - 18)
HighResB	1, 5, 9, 13, (17)

Note

As a result of the averaging process, the quality of the calculated timestamps is affected by relative changes in the internal delays of the contributing inputs. These delays are especially affected by the device’s temperature. It is strongly recommended to let the device heat up for at least 10 s before starting a measurement. Constant average count rates (averaged over the timescale of hundreds of milliseconds) will provide the best results. If you need more information on this topic, please contact us via support@swabianinstruments.com.

Data connection

The Time Tagger 20 is powered via a USB connection. Therefore, you should ensure that the USB port is capable of providing the full specified current (500 mA). A USB >= 2.0 data connection is required for the performance specified here. Operating the device via a USB hub is strongly discouraged. The Time Tagger 20 can stream about 9 MTags/s.

The Time Tagger Ultra and Time Tagger X has a USB 3.0 interface. This allows to stream up to 80 MTags/s to the PC. The actual number highly depends on the performance of the CPU the Time Tagger is connected to and the evaluation methods involved.

In addition, the Time Tagger X is equipped with both an SFP+ Port (10 GbE) and a QSFP+ port (40 GbE) which can be used for streaming up to 300 MTags/s or 1200 MTags/s respectively.

LEDs

The Time Tagger devices have LEDs showing status information.

Time Tagger X

Front panel and power button

On its front panel, the Time Tagger X has an LED inside the power button and individual channel status LEDs:

Power button LED
Color	Description
blue	Device in standby, press button to turn it on
green	Device running
orange	Device is getting ready
red	An error occurred

Channel LEDs
Color	Description
dark	Channel unavailable (according to your license)
blue	Channel available but not used by a measurement
solid green	Measurement running but no data within last 2 s
blinking green	Time tags are streamed to the PC. Blinking frequency indicates data rate
solid orange	Overflow
solid red	Error

Rear panel

LED next to the CLK IN input
Color	Description
dark	No clock signal
solid green	Valid reference or synchronization clock
solid red	Invalid reference frequency
solid blue	Ext. clock valid, but not in use

LED next to the SYNC IN input
Color	Description
dark	No synchronizer on CLK input
green	Valid signal at SYNC IN
red	Invalid signal at SYNC IN

LED next to the LOOP IN input
Color	Description
dark	No synchronizer on CLK input
green	Valid signal at LOOP IN
red	Invalid signal at LOOP IN

Time Tagger Ultra

The “Power” LED turns green when the power is supplied to the device.

Status LED
Color	Description
solid green	Firmware loaded
blinking green	Time tags are streaming
solid orange	Overflows occurred. LED turns orange for 0.3 s on overflow events. Solid orange indicates continuous overflows.
solid red	Device initialization failed (check USB connection)

LED next to the CLK input
Color	Description
dark	No clock signal
solid green	Valid reference or synchronization clock
solid red	Invalid reference frequency
solid blue	Ext. clock valid, but not in use
fast blinking red	Calibration error on at least one channel
blinking red (hardware <v1.5)	Invalid signal at SYNC IN (AUX IN 1)
blinking yellow (hardware <v1.5)	Invalid signal at LOOP IN (AUX IN 2)

LED next to the SYNC IN input (hardware >=v1.5)
Color	Description
dark	No synchronizer on CLK input
green	Valid signal at SYNC IN
red	Invalid signal at SYNC IN

LED next to the LOOP IN input (hardware >=v1.5)
Color	Description
dark	No synchronizer on CLK input
green	Valid signal at LOOP IN
red	Invalid signal at LOOP IN

Time Tagger 20

The “Power” LED turns green when the power is supplied to the device.

Status LED
Color	Description
solid green	Firmware loaded
blinking green-orange	Time tags are streaming
red	Overflows occurred. LED turns red for 0.1 s on every overflow event. Solid red indicates continuous overflows.
solid blue	Device initialization failed (check USB connection)

Test signal

The Time Tagger has a built-in test signal generator that generates a square wave with a frequency in the range 0.8 to 1.0 MHz. You can apply the test signal to any input channel instead of an external input. This is especially useful for testing, calibrating and setting up the Time Tagger initially. The Time Tagger X also provides the opportunity to put out two square wave signals with a variable frequency via the AUX Out ports on the back of the device.

Synthetic input delay

You can introduce an input delay for each channel independently. This is useful if the relative timing between two channels is important, e.g., to compensate for propagation delay in cables of unequal length. The input delay can be set individually for rising and for falling edges.

Synthetic dead time

You can introduce a synthetic dead time for each channel independently. This is useful when you want to suppress consecutive clicks that are closely separated, e.g., to suppress after-pulsing of avalanche photodiodes or as a simple way of data rate reduction. The dead time can be set individually for rising and for falling edges in each channel.

Event divider

You can introduce an event divider for each channel independently. This is useful to discard a given number of time tags before the next one is stored, e.g., to reduce the data transfer rate requirement at expense of the data accumulation efficiency. The event divider can be set individually for rising and for falling edges.

Conditional Filter

The Conditional Filter allows you to decrease the time tag rate without losing those time tags that are relevant to your application, for instance, where you have a high-frequency signal applied to at least one channel. Examples include fluorescence lifetime measurements or optical quantum information and cryptography, where you want to capture synchronization clicks from a high repetition rate excitation laser.

To reduce the data rate, you discard all synchronization clicks, except those that follow after one of your low rate detector clicks, thereby forming a reduced time tag stream. The software processes the reduced time tag stream in the exact same fashion as the full time tag stream.

This feature is enabled by the Conditional Filter. As all channels on your Time Tagger are fully equivalent, you can specify which channels are filtered and which channels are used as triggers that enable the transmission of a subsequent tag on the filtered channels.

Note

In Time Tagger 20, the software-defined input delays, as set by the method setInputDelay(), do not apply to the Conditional Filter logic.

More details and explanations can be found in the In Depth Guide: Conditional Filter.

Bin equilibration

The discretization of electrical signals is never perfect. In time-to-digital conversion, this manifests as small differences (few ps) in the bin sizes inside the converter that even varies from chip to chip. This imperfection is inherent to any time-to-digital conversion hardware. It is usually not apparent to the user. However, when correlations between two channels are measured on short time scales, you might see this as a weak periodic ripple on top of your signal. We reduce the effect of this in the software at the cost of a decrease in the time resolution by $\sqrt{2}$ . This feature is enabled by default. If your application requires time resolution down to the jitter limit, you can disable this feature.

Overflows

The Time Tagger 20 is capable of continuous streaming of about 9 MTags/s. For the Time Tagger Ultra and Time Tagger X, continuous tags streamed can exceed 80 MTags/s, depending on the CPU of the PC the Time Tagger is attached to. Higher data rates for short times are buffered internally, so that no overflow occurs. If continuous higher data rates persist, the internal buffer gets completely filled. Therefore, some of the time tags are discarded and not transferred to the PC, resulting in data loss. The hardware allows you to check with TimeTaggerBase.getOverflows() whether an overflow condition has occurred. If no overflow is returned, you can be confident that every time tag is received.

Note

When overflows occur, Time Tagger will still produce valid data blocks and discard the invalid tags in between. Your measurement data may still be valid, although your acquisition time will likely increase.

External Clock Input

Note

An alternative and more flexible way to apply an external clock signal is the use of TimeTaggerBase.setSoftwareClock(). Since software version 2.10, the software clock is recommended for applying an external clock.

Time Tagger X and Time Tagger Ultra

The external clock input can be used to synchronize different Time Tagger devices. The input clock frequency must be 10 or 500 MHz. The CLK input requires between 100 mVpp and 4 Vpp AC coupled into 50 Ohm, 500 mVpp is recommended. The lock status can be read off the LED color: If the CLK LED shines green, the Time Tagger is locked and uses the provided clock. If the LED is blue, a valid frequency is supplied, however, the Time Tagger is still configured to use the internal clocking source. In case of a wrong or unstable frequency, the LED will shine red. A 500 MHz CLK input without a Synchronizer will lead to red LEDs on LOOP IN and SYNC IN. Yet, the Time Tagger will still work normally and the LEDs can be ignored in this case.

External clock signal requirements:

The input clock signal must have a very low jitter to provide the specified performance of the Time Tagger. Please note that the timing specifications for the Time Tagger Ultra with respect to other devices on the same clock are only met from hardware version 2.3 and later.

Caution

In order to reach the specified input jitter for the Time Tagger with an external clock, the input signals must be uncorrelated to the external clock. This restriction does not exist for TimeTaggerBase.setSoftwareClock().

Time Tagger 20

The Time Tagger 20 supports software clock feature only.

Synchronization signals

Time Tagger X and Time Tagger Ultra

Up to 8 Time Tagger Ultra and/or Time Tagger X units can be synchronized in such a way that they behave like a unified Time Tagger. This requires additional hardware, the Swabian Synchronizer. The Synchronizer uses the additional hardware connections: SYNC IN, LOOP IN, LOOP OUT and FDBK OUT (see Synchronizer).

Warning

On Time Tagger Ultra units sold before September 2020, the synchronization signals use the ports labeled AUX IN 1, AUX IN 2, AUX OUT 1, AUX OUT 2. A mapping of the signal names is included in the Synchronizer documentation (see Synchronizer). If you own one of these units and would like to have a sticker to update your labels, please reach out to Swabian Instruments support .

Time Tagger 20

Synchronization of multiple Time Tagger 20 devices is not possible.

FPGA link

Time Tagger X

The Ethernet based FPGA link can be used for connecting customer’s FPGA designs directly to the Time Tagger X. The connection is provided through either SFP+ or QSFP+ connector on the back panel of the Time Tagger X. Either one of them can be active and shall be used for connection of customer’s design using either a Direct Attach Cable (DAC) or optical fiber transceiver. More details and explanations can be found in the In Depth Guide: FPGA link.

Time Tagger Ultra and Time Tagger 20

Time Tagger Ultra and Time Tagger 20 have no support for FPGA link.

General purpose IO (GPIO)

Time Tagger Ultra

Starting from the Time Tagger v2.6.6, the general purpose inputs and outputs on Time Tagger Ultra are used for synchronization signals. New Time Tagger Ultra devices will have updated labeling of these IO ports. See, Synchronizer

Time Tagger 20

The Time Tagger 20 is equipped with four general purpose IO ports that interface directly with the system’s FPGA. These are reserved for future implementations.