DE2317193B2 - FREQUENCY-VOLTAGE CONVERTER WITH HIGH ACCURACY - Google Patents

Description

The invention relates to a high accuracy frequency-voltage converter with a die Input impulses in impulses of the same energy content converting stage, one from a capacitor and a resistor existing charging circuit that can be connected to the operating voltage via a switching transistor, whose load cell constant is smaller than the smallest occurring input pulse duration, and one consisting of the same capacitor and a different resistor, through a field effect transistor effective or ineffective switchable discharge circuit, the discharge time constant of which is smaller than the The smallest occurring distance between two successive input pulses is, includes, one of the Input pulses acted upon the two transistors controlling stage and control stage one after the other an integration stage downstream of the stage converting the input pulses.

A large number of frequency-voltage converters are already known in which the input pulses using a monostable multivibrator, it is converted into square-wave pulses with constant energy content and these are fed to an integration stage or directly to a display instrument. Likewise Frequency-to-voltage converters are known which are the same for converting the input pulses into such Energy content contain a monostable multivibrator and a saturable transformer. With these and other analog converters experience conversion errors of the order of magnitude and more percent on, so that for this reason they can be used for many purposes for which the same error limit The alcohol range required is not suitable.

In another known frequency-voltage converter, the input pulses are converted in those with the same energy content with a transformer and two transistors controlled by this, of each one together with a capacitor a charging circuit and the other with the capacitor a discharge current circuit forms The two circuits are decoupled from each other by the transformer Da in such a conversion stage, a pulse with the same energy content is derived from both the rising and falling edges of each input pulse pulse doubling occurs, but this is not disruptive and in many cases is even desirable

As for the conversion error of such a frequency-to-voltage converter if it is concerned, it is well below one percent, but it is still so large that a further decrease is desirable. The remaining conversion error is mainly due to the fact that the temperature-dependent capacity of the transformer winding is included in the conversion and as a result of the Switching times of the two switching transistors when switching occurs an overlap.

Through the DT-OS 22 27 741 also known a frequency-voltage converter, which has a charging circuit with a capacitor and a field effect transistor and a discharge circuit with contains the same capacitor and another field effect transistor. The two field effect transistors are by means of a .on the input pulses applied comparator and an inverter controlled. With this converter, the input pulses are converted into a rectangular shape by the comparator Reshaped pulse train and this controls the field effect transistors so that during the duration of a Impulse of one polarity of the charging circuit is effective and the discharging circuit is ineffective and during the duration of a pulse of the other polarity the charging circuit ineffective and the Discharge circuit is effectively switched. With such a control of the field effect transistors occurs here, too, due to the switching times of the two transistors when switching over, an overlap occurs increasing the conversion error. In addition, expensive components are required for this converter

The object of the invention is to create a frequency-voltage converter in which the conversion of the input pulses in pulses with the same energy content without errors or at most with an error of a few a few per mille is feasible. In addition, the conversion stage should be as cheap as possible and with few components be constructed.

This task is based on the frequency-voltage converter of the type described above solved according to the invention in that a threshold switch with two switching points is used as the control stage is provided, which are chosen so that the blocking of the switching transistor and the conducting of the field effect transistor or the conduction of the switching transistor and the blocking of the field effect transistor with

temporal interval «follows

By this measure according to the invention, which with only a few components can be realized cheaply reliably avoided that the charging circuit and discharging circuit for a short time simultaneously are effectively switched. This has the consequence that the Conversion errors below the one-per-thousand-limit lies, so the conversion is carried out with almost no errors.

In a preferred embodiment, the to Threshold switch an input transistor, a charging or discharging circuit controlled by this with a capacitor and two switching transistors, the base-emitter path of which is connected to the output of the Charging or discharging circuit and, on the other hand, connected to different points of a voltage divider are.

The invention will be explained in more detail with reference to the drawing, which contains an exemplary embodiment

The frequency-to-voltage converter includes a stage μ I, in which the input pulses 2 are converted into pulses 3 with the same energy content, and one of the conversion stages 1 downstream integration stage 4, which is constructed in a known manner and not detailed is shown. A direct voltage appears at output 5 of the integration stage 4, the amount of which is proportional the pulse repetition frequency of the input pulse is 2

The conversion stage 1 consists of a charging circuit 6 and a discharging circuit 7 are decoupled. The charging circuit 6 includes a switching transistor 8, a capacitor 9 and a Resistor 10. Between the capacitor 9 and the resistor 10 on the one hand and the output terminal 11 the conversion stage 1 on the other hand, a further resistor 12 is connected to the field effect transistor 13 and the capacitor 9 form the discharge circuit 7.

A threshold switch 15 is used to control the switching transistor 8 and the field effect transistor 13 provided with two switching points. As can be seen, the threshold switch 15 consists of an input transistor 16, a charging or discharging circuit 17 a capacitor 18 and two switching transistors 19 and 20, the base-emitter path each with the Output of the charging or discharging circuit 10 and with different points 21 and 22 of a voltage divider 23 is connected

To explain the mode of operation of the converter, it is assumed that the capacitor 18 is charged is and therefore the transistors 19 and 20 are in their conductive state. As a consequence, that the transistor 8 is conductive and the field effect transistor 13 is in its blocking state. The capacitor 9 is charged.

As soon as a positive pulse appears at the base of transistor 16, iier transistor is blocked and the capacitor 18 discharges tangentially through the resistors 24 and 25. Since the emitter of the transistor 19 is at a lower negative potential than that of the transistor 20, is after one by the discharge of the capacitor 18 for a certain time, the transistor 19 is blocked first Transistor 8 is controlled in its blocking state, so the charging circuit is switched ineffective. To If a further period of time has elapsed, the transistor 20 is also blocked, and consequently the field effect transistor 13 is controlled in its conductive state and thus the discharge circuit is effectively switched. Of the Capacitor 9 now discharges quickly through resistor 12 and at the input of the integrator an impulse appears.

If the input pulse at the base of transistor 16 disappears again, this becomes conductive in its State controlled As a result, the capacitor 18 is charged via the resistor 24. Due to the different emitter bias voltages of the transistors 19 and 20, the transistor 20 is first conductive and the field effect transistor 13 blocked - the discharge circuit is switched ineffective - and after one through the capacitor 18 and the resistor 24 certain period of time the transistor 19 is conductive and thus also the transistor 8 Charging circuit 6 switched effective and the capacitor 9 charged quickly. Due to this, appears on Input of the integration stage a further pulse.

With a constant operating voltage Ub and provided that the charging time constant of the charging circuit 6 is smaller than the smallest occurring input pulse duration and the discharging time constant of the discharging circuit 7 is smaller than the smallest occurring distance between two successive input pulses, the pulses resulting from the charging or discharging of the capacitor 9 have the same energy content in each case. If the resistors 10 and 12 are also selected to be of the same size, the energy content of the impulses produced when charging the capacitor 9 and those of the impulses produced during discharge are also the same. The latter, however, is not absolutely necessary for the converter to work properly.

1 sheet of drawings

Claims (2)

Patent claims: 1. Frequency-to-voltage converter of high accuracy with a cfie input pulses to pulses the same energy content converting stage, which consists of a capacitor and a resistor existing charging circuit, which can be connected to operating voltage via a Schakt transistor Loading time constant smaller than the smallest occurring Input pulse duration, and one from the same capacitor and a different resistor existing discharge circuit that can be switched effectively or ineffectively by a field effect transistor, whose discharge time coefficient is less than the <s smallest occurring distance between two successive input pulses is, includes, oneF of the Input pulses acted upon the control stage, which controls the two transistors one after the other and an integration stage downstream of the stage converting the input pulses, d a through characterized in that a threshold switch (15) with two thresholds is used as the control stage different response levels are provided which are selected so that the blocking of the Switching transistor (8) and the becoming conductive of the field effect transistor (13) or becoming conductive of the switching transistor (8) and the blocking of the field effect transistor (13) with a time interval he follows. 2. Frequency-voltage converter according to claim 1, characterized in that the threshold switch (15) an input transistor (16), a charging or discharging circuit (17) controlled by this, the has a capacitor (18) and at least one resistor (24, 25), as well as two switching transistors (19, 20), the base of which is attached to the Ladebzw. Discharge circuit (17) and its emitter different points (21,22) of a voltage divider (23) are connected.