LV13662B - Device for measuring amplitudes of short single pulses - Google Patents

Abstract

The device is related to measurement technique and can be used for measuring amplitudes of single nano-second pulses received from photo-detectors. The method of amplitude-to-time conversion, which is based on the conversion of measured pulse amplitude into a time interval proportional to the pulse amplitude, is realized in the device. The aim of the invention is to increase stability of the device and reduce its "dead" time. To achieve this aim, additional charge from the output of the time interval former (6), through the feedback capacitor (5), is given to the capacitor (2). The charge generated at the leading edge of the time interval makes the switching of the time interval former (6) more stable and without oscillations. The charge generated at the leading edge of the time interval improves stability of the device and decreases its "dead" time. Additionally, the stability of the device operation becomes higher due to building the time interval former on the basis of a comparator (8) with the threshold level correlated with the drift of initial voltage across the the diode (1). By measuring amplitudes of pulses from photo-detectors, the impact of their intrinsic amplitude-dependant delays can be compensated so as to elevate the measurement accuracy, for example, in laser ranging.

Description

The proposed device relates to a measuring technique and can be used to measure the amplitude of signals emitted from photo receivers. Pulse amplitude studies refer to basic measurements in 10 pulse techniques. The most complex is the measurement of the amplitude of single short (nanosecond) pulses [1]. A method for measuring short pulse amplitudes based on the conversion of voltage pulses to quasi-DC voltage is known [1]. Devices implementing this method extend the pulse duration with a diode-capacitor type accumulator, and the amplitude of the extended pulses is further measured. The main disadvantage of these devices is their limited functionality, since before each subsequent input pulse amplitude, the recorder has to be installed and maintained in its initial state.

There is also a known method of measuring single pulse amplitude using a "amplitude-time" conversion, which results in the amplitude of the measured pulse being converted to a proportional time interval [1]. Amplitude measurement in this case is reduced to measuring this time interval, which can be done with great precision. The device implementing this method [2] is technically very close to the proposed device because it contains an input resistor (the resistor serves both for cable load matching and capacitor recharging), diodes, capacitors, power generators, time interval formers and timers, which converts the time interval into code.

According to the prototype circuit operating algorithm, the device automatically returns to its original state after each input pulse and thereby advantageously differs from the analog. The main drawbacks of the 25 prototype are its low stability and high "dead time". The low stability of prototype performance is measured by measuring amplitudes close to the sensitivity of the device. In this mode, due to the influence of noise, the interval builder can generate several pulses in succession at the output. The generation of the interval shaper is also possible in the final phase of the interval shear, when a small slope signal is applied to the inlet of the shaper. As for the large "dead time", this deficiency is present in any 30 amplitude-time converter.

The object of the invention is to increase the stability of the device and to reduce the "dead time".

A schematic diagram of the proposed device according to the measurement of negative input pulses is shown in Figs. 1 (for positive input pulses the polarity of the diode connection and the polarity of the current generator are reversed). The device comprises: diode 1, capacitor 2, power generator 3, input resistor 4, feedback capacitor 5, time interval generator 6 and timer 7. Device input is connected to input resistor (4) and connected to diode (1) via a capacitor (2), with a power generator (3) and an input to the interval formator (6), the output of the interval generator (6) being connected to a timer input (7) whose output is also the output of the device but the feedback capacitor (5) connects the output of the interval maker (6) to its input.

Fig. 2 is a schematic diagram of an interval shaper comprising a comparator (8), a buffer amplifier (9) and an integrated RC circuit (10). The direct input of the comparator (8) is the input of the interval builder (6), but the direct output of the comparator (8), which is also the output of the interval maker (6), is connected via a buffer amplifier (9) and an integrated RC circuit (10) (8) inverse input.

Fig. 3 shows operation time diagrams of the proposed device, where: А - input signal diagram; В - signal diagram on the capacitor (2), C - signal diagram at the outputs of the interval generator (6).

Operation of the device (Fig. 1)

In the initial state, the diode (1) is open and positive current flowing through it from the current source (3) provides an initial voltage to the capacitor (2) equal to the voltage drop on the open diode (1). Upon receiving a short pulse with negative polarity (see A-diagram in Fig. 3) and with an amplitude U at the input of the device, the capacitor (2) is quickly recharged through the open diode (1) and the input resistor (4). The capacitance of the capacitor (2) is selected such that its recharging time approximates to the front pulse front (1-2 ns). As a result, the voltage on the capacitor (2) changes by an amount equal to the input pulse amplitude U, as shown in B-diagram in Fig. 3.

At the end of the input pulse the diode (1) closes and the inverter voltage range starts. At the same time, the linear linear capacitor (2) is charged slowly and the circuit returns to its original state, as can be seen from the time B-diagram in Fig. 3.

The voltage from the capacitor (2) arrives at the input of the interval shaper (6). When the voltage on the capacitor (2) reaches the threshold of the interval shaper (6), it is actuated and a time interval is created at the output (C-diagram in Fig. 3), the duration of which is proportional to the input pulse amplitude. The timer (7) converts the duration of this interval to a numeric code. During the two edges of the formed interval, additional charge arrives through the feedback capacitor (5) to the capacitor (2). The charge generated by the front edge of the time interval provides a more stable start in the mold (6) without generation. The additional charge corresponding to the trailing edge of the output interval not only provides a more stable start in the molded (6) but also accelerates the restoration of the circuit to its original state and thus reduces the "dead time" of the device shown in C-diagram (Fig.3). with a broken line.

Operation of the interval maker (Fig.2)

The voltage from the capacitor (2) goes to the direct input of the comparator (8). When the voltage on the capacitor (2) reaches the comparator threshold (diagram В Fig.3), the comparator (8) is actuated and a pulse output is generated at its output proportional to the magnitude of the pulse to be measured. The comparator threshold is set at the inverter input of the comparator (8). For this purpose, the same voltage is applied to this input via the dividing buffer amplifier (9) as to its direct input, but balanced by the integrated RC-circuit (10), i. the comparator threshold level is correlated with the initial voltage across the capacitor (2). The comparator (8), which responds only to the voltage difference between its inputs, compensates for the slow change in the initial voltage on the capacitor (2), which increases the operational stability of the device. By changing the time constant of the RC-circuit (10), the linearity of the conversion function can be changed to some extent. If the time constant is much larger than the conversion time, the conversion function will be close to linear, but if the time constant is comparable to the conversion time, this function acquires a logarithmic character, i.e. the meter will become less sensitive to high amplitude input signals.

The proposed device is distinguished by higher operational stability and reduced "dead time". During the actuation moments of the interval shaper (6), corresponding to the front and the rear front of the formed time interval, additional charge arrives through the feedback capacitor. The charge generated by the front edge of the time interval increases the stability of the start of the interval maker without generation. The charge generated by the trailing edge of the time interval not only provides a more stable start of the interval shaper (6), but also accelerates the restoration of the circuit to its original state and thus reduces the "dead time" of the device. The performance stability of the device is also improved due to the compensation of the low frequency oscillations of the temperature and the output voltage on the diode (1), as the threshold level of the comparator (8) is correlated with the slow change of the initial voltage.

Measuring the pulse amplitudes emitted from the photodetectors can compensate for the effects of the internal delays of the photodetectors, and can increase the accuracy of the measurements, for example with laser rangefinding.

Sources of information

1. Кукуш В.Д. Электрорадиоизмерения. M., Radi я з з ь ь, 1985, с. 137-141.

2. Yu. Artyukh, V. Bespal'ko, К. Lapushka, A. Ribakov Digital Range-Bias Correction of SLR Station Riga-1884. Proceeding of the 12 ^th International Workshop on Laser Ranging. Matera, Italy, 13-17 November 2000

Claims (2)

Claims 1. a short single-pulse amplitude measuring device comprising an input resistor, a diode, a capacitor, a current generator, a time interval generator and a timer, wherein the input of the device is connected to an input resistor and through a diode to a capacitor, a current generator and an the interval-shaped output is connected to a timer input, and the timer output is the output of the entire device, which is different in that it includes a feedback capacitor that connects the interval-maker output to its input. The device according to claim 1, characterized in that the time interval formator comprises a comparator, a buffer amplifier and an integrating RC-circuit, wherein the direct input of the comparator is simultaneously the input of the interval maker and the direct output of the comparator which is also the interval maker. output, via a buffer amplifier and an integral RC-circuit, is connected to the inverter input of the comparator.