Time to Amplitude Converter

from Wikipedia, the free encyclopedia

A Time to Amplitude Converter (TAC) is a device that generates an output signal with an amplitude proportional to the time interval between input “start” and “stop” pulses. The amplitude distribution of the output pulses is then usually recorded by a multichannel analyzer ( multichannel analyzer ). It is therefore a measure of the distribution of the time intervals between the start and stop pulses and is often referred to as the “time spectrum”.

The Time to Amplitude Converter was invented by Bruno Rossi in 1942 to determine the decay time of the muon .

The great popularity of the TAC for the measurement of time intervals results from the wide availability of multichannel analyzers in most measurement laboratories. By converting the time interval into a pulse amplitude proportional to it, a TAC allows the use of different methods for analyzing and storing the pulse amplitudes as a substitute for the direct measurement of the time interval. One of the most important properties of the TAC is the linearity of the conversion ratio between time interval and amplitude. To test this linearity, it is necessary to introduce fixed delays of known magnitude between the start and stop pulses. For time periods of up to a few hundred nanoseconds, this can be achieved, for example, by using coaxial cables of different lengths.

Two different types of TACs are known:

  • The overlap type is based on measuring the overlap between the supplied (rectangular) start-stop pulses. If these two impulses match, there is a complete overlap; if, on the other hand, they are a pulse width apart, there is no overlap. Therefore, the Time to Amplitude Conversion (TAC) is performed when an output pulse has been generated whose amplitude includes the overlap area. The main advantage of this type of TAC is that it allows very fast measurements compared to other methods. In contrast, the linearity of the conversion ratio between time interval and amplitude is rather poor, so this type is mainly used when the main focus is on maximum counting rates.
  • With the start-stop type, the start pulse activates a circuit that z. B. leads to the charging of a capacitor by a constant current source . This continues until the stop pulse arrives. The constant current generates a linearly increasing voltage in the capacitor. This type has a much better linearity and is therefore often used for measurements with lower count rates.

Individual evidence

  1. ↑ George W. Clark: Bruno Benedetto Rossi National Academic Press, Washington DC 1998, p. 13

swell

  • [Glenn F. Knoll, Radiation Detection and Measurement]

See also