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.
The table below lists various pulse inverters available in the market that have been tested or are expected to work with the Time Tagger 20.
| Inverter model | Bandwidth | Tested with TT20 |
| INV-0026 | 1 MHz - 26.5 GHz | Works with MPD SPAD NIM output.Recommended option. |
| INV-0040 | 1 MHz - 40 GHz | Not tested. Expected to work well. |
| INV-0065 | 1 MHz - 65 GHz | Not tested. Expected to work well. |
| A-PPI-D | Unknown | Works with MPD SPAD NIM output. |
| SI100 / SIA400 | Unknown | May work depending on pulse duration. Some customers reported problems when using it with TT20. |