DE2227741A1 - Method and circuit arrangement for the precise measurement of the frequency of an electronic signal. . Note: Honeywell Information Systems Inc., Waltham, Mass. (V.StA.) - Google Patents

Description

Dipl.-Ing. Heinz Bardehl ©

Patent attorney O O O T 7/1 MüocIkr 22, Hermstr. 15, part. ? 92555 ILL II 4 I Postal address Munich 26. Postftch 4

χ 7th law in 1972

My reference: P 1399

Applicant: Honeywell Information Systems Inc. 200 Smith Street
Waltham / Mass., V. St. v. A.

Method and circuit arrangement for the precise measurement of the frequency of an electronic signal

The invention relates to electronic measurement circuits and in particular to an analog precision frequency measuring circuit, the frequencies in the range of 0 to 100 Hertz allowed to measure.

Up to now, electronic frequency measurement methods have been used in tachometers, such as those used in automobiles will. In these known methods, a circuit is typically used that is used with each recording of an input pulse controls a monostable circuit which generates a pulse of almost constant pulse width and almost constant pulse height. The DC mean value of the pulse train composed of these pulses becomes Used to display the input frequency.

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Accordingly, in previously known systems, a fixed predetermined current is over during a fixed period of time a low-pass filter is fed to a capacitor. To get an output signal that is linear to the input frequency is proportional, an integrator is used in a known method, which is switched on by a pulse the next pulse carries out an integration and which is then switched off. This procedure leads to Output of a voltage that is proportional to the distance between the two events or processes. By measuring the The frequency is determined in the time span between these two events or processes.

A major disadvantage of this system is that in the event that the time is close to zero, the relevant

to system for the delivery of an infinite number of results and / one The display tends to be inaccurate, or even no measurement is taken at zero frequency. Another disadvantage of the known systems is that two variables, voltage and time, must be precisely controlled. Accordingly, in addition to an accurate power source, an accurate clock or clock generator is required. These two bodies also require an exact initial calibration. Yet another disadvantage of the known systems lies in the difficulty of obtaining pulses with very fast rise and fall times, such as those for square waves, which are actually rectangular are required.

The invention is accordingly based on the object to provide a measuring circuit which, while avoiding the above identified difficulties in operation is reliable

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down to a frequency of zero and which, moreover, has fewer components, requires a minimum of calibration and relatively easy and waste to manufacture and maintain leaves.

The object indicated above is achieved by the invention specified in claim 1. According to the invention is an analog precision frequency measuring circuit for the precise frequency measurement of an electronic signal created, the is characterized by

a) that a first electrical storage device is provided, which to a certain amount of electrical charge able to save

b) that with the first electrical storage device, a switching device is connected to the electronic Signal to alternately charge the first electrical storage device at a certain speed and allowed to unload,

c) that with said switching device and the first electrical storage device a second electrical Storage device is connected, which is then able to absorb the specific amount of electrical charge in each case, how to discharge the first electrical storage device will, and

d) that a converter device is connected to the second electrical storage device, which is of the said electrical storage device, the amount of electrical charge absorbed into an electrical voltage implements.

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An analog frequency measurement circuit according to the invention allows an unknown frequency of an incoming Measure the signal of an electronic circuit by emitting an output voltage that is linearly proportional to the occurring frequency. The incoming frequency signal is converted into square-wave pulses using methods known per se reduced. The relevant incoming signal then alternately triggers two electronic switches, the the charge of a certain value of a capacitor from an exact voltage source as well as the discharge of the relevant one Allow capacitor, according to the frequency of the incoming signal. One connected to the capacitor Circuit transfers an exact amount of charge per cycle to an RC circuit · In this way, the RC circuit becomes a current supplied, and thus the voltage appearing at the resistor in question is proportional to the number of input signal periods per second.

The invention is explained in more detail below using an exemplary embodiment using a drawing.

In the analog frequency measuring circuit shown in the drawing a precision voltage source 100 is provided, which consists of a voltage stabilizer and a There is a supply voltage setting divider. The roughly stabilized supply voltage source is at the connection point 31 at one Resistor 1 connected, which typically has a resistance of 600 ohms. It should be noted that any other suitable resistor can also be used here. The resistor 1 in question is connected to the anode of a ZENER diode 3 at connection point 2. the

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The cathode of the ZENER diode 3 is connected to earth 4. Of the The supply voltage setting divider consists of a voltage divider comprising a resistor 5 and a resistor 7. One end of the resistor 5 is connected to the connection point 2, and the other end of the resistor 5 is connected to a connection point 6, to which one end of the resistor 7 is connected «Das the other end of the resistor 7 is connected to earth 8.

With the output of the precision voltage source. 100 an electronic switch 101 is connected. This switch 101 contains an input terminal 110 which is connected to the anode of a diode 12. The cathode of the diode 12 is with the gate electrode of a field effect transistor 11 is connected. A connection point 10 between the cathode of the diode 12 and the gate electrode of the field effect transistor 11 is connected to the source electrode of the field effect transistor via a resistor 9 11 connected. The drain electrode of the field effect transistor 11 is connected to a connection point 13, between which and earth 15 is a capacitor 14, the one typical capacitance value of 0.01 / uF. It should be noted here that a capacitor 14 with any other suitable capacitance value can be used.

A second switch 103 is connected to the memory element 102; this second switch 103 is connected to the connection point 13. The relevant second switch 103 contains an input terminal 120 which is connected to the anode of a diode 20. The cathode of the diode 20 is with the gate electrode of a field effect transistor 16 is connected. At one between the cathode of the diode 20 and the gate

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Electrode of the field effect transistor 16 provided connection point 17 is a resistor 18 with its one End connected; the other end of resistor 18 is connected to ground 19. The source electrode or source of the field effect transistor 16 is connected to the connection point and the drain electrode or sink of the field effect transistor 16 is connected to a circuit 104 consisting of a low-pass filter and an amplifier. The sink

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of the field effect transistor / is connected to the connection point with the low-pass filter and the amplifier mentioned. The circuit 104 comprising the low-pass filter and the aforementioned amplifier contains an operational amplifier 23 (as already described elsewhere: US application, Serial No. 52 035). The operational amplifier 23 is connected with its inverting input terminal 26 (minus sign) to the connection point 21. The non-inverting input terminal 22 (plus sign) of the amplifier in question is grounded. A parallel RC element consisting of a resistor 24 and a capacitor 25 is connected in parallel to the operational amplifier 23 by being connected to the connection terminals 21 and 27.

In the table given below, typical values of the individual elements are given which are within the scope of the invention to be used. It should be noted, however, that the invention is not limited to these values, but rather that other suitable values than lying within the scope of the invention can also be selected.

Tabel

Component value unit

Resistance 1 600 Ohm Resistance 5 1800 Ohm Resistance 7 5000 Ohm Resistance 9 2,200,000 Ohm Capacitor 14 0.01 Microfarads Resistance 18 1.00 Megohm Resistance 24 1.00 Megohm Capacitor 25 2.00 Microfarads ZENER diode 3 6.8 volt

A comparator 202 has its inverting input connected to an input terminal 200, and that is not inverting input of comparator 202 is grounded · The comparator is also connected to input terminal 110 of the switch 101 connected. An inverter 204 with its inverting input is also connected to the relevant input terminal 110 connected; the non-inverting input of the inverter 204 is grounded. The relevant inverter 204 is also connected to the input terminal 120 of the switch 103 is connected.

With regard to the mode of operation of the circuit arrangement according to the invention, it should be noted that a signal 201 is unknown Frequency is converted into a square wave signal 203, unless it is already in this form. The person in question Signal conversion is carried out by means known per se, such as by the comparator 202 (see in this regard U.S. patent application serial no. 34 934 of 5.7.70 and also U.S. Patent 3,217,173). The square wave signal

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is fed to the input terminal 110 of the electronic switch 101 and then fed to the inverter 204, which is connected to the Input terminal 120 of switch 103 emits the complementary signal 205. The sequence of operations of the frequency measuring circuit is the following: If there is a potential at terminal 110 or 120 of + 12V prevails, then either the field effect transistor 11 or the field effect transistor 16 is non-conductive Condition pre-tensioned. If the potential at one of these terminals is lowered to -12 V, the corresponding Field effect transistor conductive. When the input signal 201 becomes negative, the potential at the first switch terminal drops 110 to -12 V, while the potential at the second switch terminal 120 rises to +12 V. The switch 101 becomes conductive, while switch 103 becomes non-conductive. A constant voltage of 5 volts is supplied by the precision voltage source 100 impressed on the capacitor 14, which takes a charge of approximately 0.05 microcoulombs at a capacitance value of 0.01 / uF in the present embodiment. With the next input signal transition, the potential at the control terminal for switch 101 rises to +12 V, while the Potential at the control terminal for switch 103 drops to -12 V. Accordingly, the switch 103 is in the conductive state State while the switch 101 is in the non-conductive state. When the two switches are in this state, the Operational amplifier 23 fixes the voltage on capacitor 14 and controls this voltage to 0 by following the procedure below described manner allows a current to flow through the capacitor. The charge on the capacitor 14 is thereby dissipated that both terminals 13 and 15 are grounded. Terminal 15 is already grounded, and terminal 13 can be be grounded by that they are via the field effect transistor

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is connected to terminal 21. The inverting input 26 of the operational amplifier 23 has an ideal It has an infinite impedance and therefore does not draw any current from terminal 21. The operational amplifier 23 works but in such a way that it lowers the voltage at the connection point in such a way that it coincides with that at the connection point 22, which is already grounded. This is done by the amplifier in question by changing the voltage Connection point 27 is set so that a current through the capacitor 25 and the capacitor in series 14 is conducted until the voltages at the connection points 21 and 13 each reach ground potential. If this happens, the capacitor 14 is fully discharged, and is the same current required to discharge the capacitor flowed through the capacitor 25 during the same period. There is thus a charge on the capacitor 25 has been transferred, which corresponds to the charge on the capacitor 14. Accordingly, there is one per cycle or per period Transferred fixed charge from the capacitor 14 to the capacitor 25 out. The more periods there are per time unit are, the more charge is transferred per unit of time. Accordingly, the current is proportional to the number of periods per second.

If this process is sufficient to complete it If time has passed, the potential increases. the second switch 103 to +12 V again, and the circuit is thus for another period ready. Assuming that all time constants and duty cycles or duty cycles are in are chosen appropriately (with the component values given in the table above for this particular embodiment are the correct component values) and that the

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When the frequency of the switch control input signal is not excessively high, the same amount of charge (about 0.05 microcoulombs) is transferred to the capacitor 25 in each cycle. If one also assumes that F cycles or periods of the switches occur per second, then the amount of charge transferred to the capacitor 14 in one second is F * 0.05 microcoulombs, which is equal to an average current of 0.05 F microamps is. This current of 0.05 F microampere leads to the slow discharge via the resistor 24 and thus supplies an average output voltage Eq ^ of 0.05 F volts. Here, F means the frequency that is measured.

It should be apparent that the scale factor of this circuit in volts (output signal) per Hertz (input signal) insensitive to all parameters with the exception of the resistance value of the feedback resistor 24, the Capacitance of capacitor 14 and the stabilized 5 volt precision voltage source used in charging capacitor 14 100 is. The size of the capacitance of the capacitor 1 4 only affects the time constant and the Ripple of the output signal. In general, the AC ripple component of the output signal is one Sawtooth wave having a peak-to-peak amplitude equal to that multiplied by the capacitance of capacitor 14 and the amplitude of the stabilized 5 volt supply voltage divided by the capacitance of the capacitor 25. the Output signal peaks caused by switching transitions can be reduced by adding a resistor (not shown) is provided between the drain of the field effect transistor 16 and the input of the operational amplifier 23.

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The voltage stabilizer part of the precision voltage source 100 outputs a voltage of to the supply voltage setting divider of the relevant precision voltage source 6.8V. This voltage is in the supply voltage divider stepped down to 5 V. A voltage of 6.8 V was chosen as the output voltage of the voltage stabilizer, because it happens that this voltage value is at an average voltage point for the ZENER diode with regard to temperature changes. The output voltage of the The voltage source is further reduced to 5 volts by the voltage divider comprising the resistors 5 and 7. The correct choice of resistors to deliver an accurate voltage of -5 V is the only calibration that is in the system is required.

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Claims (12)

Claims 1.j method for the precise measurement of the frequency of an electronic signal, characterized . a) that a first electrical storage device (14) during each complete period of the electronic A certain electrical charge is alternately applied to the signal and discharged, b) that the discharge of the first electrical storage device (14) discharged! «Was correct electrical charge during the respective period of the electronic Signal is transmitted to a second electrical storage device (25) and c) that the charge transferred per unit of time in an eOektisdie Tension is implemented. 2. Analog circuit arrangement for the precise measurement of the frequency of an electronic signal, in particular for Implementation of the method according to claim 1, characterized in that a) that a first electrical storage device (14) for storing a certain amount of electrical charge is provided, b) that switching devices (101, 103) are connected to the first electrical storage device (14) which controlled by the electronic signal, the first electrical storage device (14) with a specific Allow speed to alternate between loading and unloading, c) that with the switching devices (101, 103) and the first electrical storage device (14) a second electrical storage device (25) is connected to the respective discharge of the first electrical storage device (14) the specific 209851/0901 able to absorb electrical charge, and d) that with the second electrical storage device (25) a conversion device (23) is connected, the from the relevant electrical storage device (25) converts the amount of electrical charge absorbed into an electrical voltage. 3. Circuit arrangement according to claim 2, characterized in that the number of discharges of the first electrical Storage device (14) is controlled per unit of time by the switching devices (101, 103) and that the Switching devices (101, 103) are switched on and off alternately at a speed which is almost is equal to the frequency of the electronic signal. 4. Circuit arrangement according to claim 2 or 3, characterized in that transmission devices (16) are provided are that the electrical charge from the first storage device (14) to the second electrical Transfer memory device (25) out. 5. Circuit arrangement according to claim 4, characterized in that the transmission devices by a Operational amplifiers are formed. 6. Circuit arrangement according to one of claims 2 to 5 »characterized in that with the first electrical Storage device (14) one used to charge it, a constant voltage output voltage source (100) is connected. ? 0 9 R 5 1 / f) 9 0 1 7. Circuit arrangement according to one of claims 2 to 6, characterized in that the switching devices (101,103) Semiconductor diodes (12, 20) included. 8. Circuit arrangement according to one of claims 2 to 6, characterized in that the switching devices (101,103) each contain a semiconductor diode (12; 20) and a transistor, the base of which with the cathode of the diode (12; 20) is connected, the emitter of which is connected to the first electrical storage device (14) and its collector is connected to the second electrical storage device (25). 9. Circuit arrangement according to claim 8, characterized in that the transistors are each provided by a field effect transistor (11, 16) are formed. 10. Circuit arrangement according to claim 8, characterized in that a transistor is of the npn conductivity type and that the other transistor is of the PNP conductivity type. 11. Circuit arrangement according to one of claims 2 to 10, characterized in that the memory devices (14, 25) are formed by capacitors. 12. Analog circuit arrangement for precisely measuring the frequency of an electronic signal, in particular for performing the method according to claim 1, characterized marked, a) that a first capacitor (14) is provided for storing a certain amount of electrical charge, 2 0 9 8 5 1 / f) 9 0 1 222774Ί b) that with the first capacitor (14) a one constant voltage-emitting voltage source (100) is connected for charging, c) that a first switching device (101) is provided, to switch between an electrical on and off state in response to the occurrence of the electronic signal capable and provided between the first capacitor (14) and the voltage source (100) and in the on-state causes the charging of the first capacitor (14), d) that a second capacitor (25) is provided for storing a certain amount of electrical charge, e) that a second switching device (103) is provided which reacts to the occurrence of the electronic signal able to switch between an electrical on and off state and between the second Capacitor (25) and the first capacitor (14) connected is, f) that with the first capacitor (14) and the second Capacitor (25) an operational amplifier (23) is connected to the electrical charge of the first Capacitor to the electrical charge on the second capacitor (25) in each case in the event that the second switching device (103) is switched to the on-state, and g) that with the second capacitor (25) a conversion device (23) is connected, which the electrical charge absorbed by the second capacitor (25) in converts an electrical voltage. 1/0901 Blank page