PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
OF THE ORDER OF THE OCTOBER REVOLUTION AND THE ORDER
OF THE RED BANNER OF LABOR
named after S. M. Kirov

Volume 278 1975

TIME-AMPLITUDE CONVERTER-CHRONOTRON

V. A. Avdeev, V. M. Kuznetsov

(Presented by the scientific and technical seminar of the High-Energy Laboratory of the Research Institute of Nuclear Physics)

In experimental nuclear physics, various types of time-amplitude converters with high time resolution are widely used.

The article describes the possibility of using a multichannel chronotron as a time-amplitude converter in the study of relatively narrow time-of-flight spectra.

A time-amplitude converter based on a multichannel chronotron is characterized by high differential and integral linearity, stability of the measurement scale and of the zero of the readout scale. A certain drawback of it is the comparatively narrow measurement range, which is associated with the practically limited number of chronotron channels.

Figure 1 shows the block diagram of the converter. Pulses arrive at the “start” and “stop” inputs of the shapers $\Phi_1$, $\Phi_2$; the time interval $\tau$ between them must be measured and recorded in the channel of the amplitude analyzer corresponding to this interval. The “stop” pulse shaper forms a negative strobe pulse with a duration equal to the measured time range. The strobe pulse controls the gate $K$, which passes the “start” pulse during the action of the strobe pulse. In addition, the strobe pulse is fed to the “NOT” inverter, from whose output a positive pulse is applied to the “inhibit” inputs of the anticoincidence circuits $AC_1 \div AC_n$. The “inhibit” inputs of the anticoincidence circuits are connected to one another in series through delays whose total electrical length is equal to the measured time range. The “start” pulse, passing through gate $K$, is applied to the other inputs of all the inhibit circuits simultaneously (without delay relative to one another). The operating principle of the device is that, depending on the instant of arrival of the “start” pulse relative to the “inhibit” strobe pulse, the “start” pulse passes to the outputs only of those anticoincidence circuits at whose “inhibit” inputs the leading edge of the “inhibit” pulse has not yet arrived. Thus, if the “start” signal arrives simultaneously with the beginning of the strobe signal, all anticoincidence circuits operate; if the “start” pulse is delayed relative to the leading edge of the “stop” signal by a time greater than the measured range of the chronotron, then none of the “inhibit” circuits operates.

Thus, the delay time of the “start” pulse relative to the leading edge of the “stop” signal is converted into a number $n$ of operated “inhibit” circuits proportional to this time. For conversion of the number

Fig. 1.

…of triggered circuits into the amplitude of the output pulse, all outputs of the “inhibit” circuits are connected through resistors \(R_1 \div R_n\) to a common load, as a result of which all signals are summed.

Thus, the amplitude of the device output pulse is proportional to the number of triggered chronotron circuits and, consequently, to the time interval between the “start” and “stop” input signals.

Figure 2 shows the schematic diagram of an anticoincidence element together with the “NOT” inverter. An ordinary coincidence circuit [1], opened at the “inhibit” input (\(T_4\)) by a constant bias of \(-0.5\ \text{V}\), is used as the anticoincidence circuit. A positive pulse is fed to this input from the “NOT” element (\(T_1—T_3\)), and this effects the “inhibition.” In the absence of an “inhibit” signal at the inverter input (a negative pulse), the arrival of a negative pulse at input 2 of the “inhibit” circuit causes it to trigger. The inverter is made as a transistor current switch (\(T_1—T_2\)). Transistor (\(T\)) is used to match the potential levels of the input of the inhibit circuit and the output of the inverter. As the key, the coincidence circuit described earlier [1] is used.

Fig. 2.

The shapers \(\Phi_1,\ \Phi_2\) are made according to the identical circuit shown in Fig. 3. The output pulses of the shaper have a rigid time reference with respect to the peak of the input pulses. The input negative pulse is applied to the bases of the transistors of the current switch \(T_1,\ T_2\). In this case, the pulse arrives at the base of transistor \(T_1\) through delay line \(LZ_1\). Bipolar current pulses are formed in the collector circuits of transistors \(T_1,\ T_2\). The instant at which these pulses pass through zero is strictly fixed with respect to the peak of the input pulse \((t_{\text{imp}})\) and is determined by the following equality:

\[ t_1 = t_{\text{imp}} + \frac{\tau_{\text{del}}}{2}, \tag{1} \]

where \(\tau_{\text{del}}\) is the delay value of line \(LZ_1\).

It follows from expression (1) that the instant at which the bipolar pulse crosses zero does not depend on the amplitude of the input signal. The one-shot multivibrator on tunnel diode TD\(_1\), whose operating point is chosen near the peak of the diode current–voltage characteristic, is triggered at the instant when the bipolar pulse crosses zero. This determines the time reference of the output pulse. The TD\(_1\) one-shot multivibrator controls an output current switch on transistors T\(_3\), T\(_4\). The output pulse is taken from the emitter follower T\(_5\). Experimental verification showed that, when the input signal changes by 20 dB, the time shift of the output pulse is no more than \(\pm 0.5\) ns in the range of input-signal durations from 10–20 ns. The shaper ensures operation at load rates up to \(10^8\) pulses/s.

Fig. 3.

A sixteen-channel time-amplitude converter–chronotron has been practically developed and experimentally tested. The minimum time resolution of the converter is \(\sim 0.2\) ns. The converter is used to record the energy spectrum of neutrons in the reaction of photoproduction of \(\pi^+\)-mesons on protons \(\gamma + p \to \pi^+ + n\). Kinematic calculation of the neutron time of flight determined the required measurement range \(\Delta t_{\text{meas}} = 12\) ns. To cover this range, the time resolution of the chronotron (discreteness) was chosen to be 1 ns, which provides a time-of-flight measurement range equal to 16 ns.

LITERATURE

1. V. A. Avdeev, V. M. Kuznetsov, Pribory i tekhnika eksperimenta, 3, (1971).