JPH0635195Y2 - Time interval measuring circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to improvement of integrated current adjusting means in a time interval measuring circuit.

<Prior Art> As a time interval measuring circuit, which does not require an A / D converter and is easy to adjust, there is a time expansion type time interval measuring circuit as shown in FIG. The operation will be described based on the time chart of FIG. Here, as a design example, the current values of the constant current sources 4, 5 and 6 are respectively 1024 μA and 3
2 μA and 1 μA, and the capacitance of the capacitor C is 84 pF.

(1) Time interval to be measured by the control output of the control circuit 8
The current switch 1 is closed for T _{1 to} T ₂ and the capacitor C is charged with 1024 μA.

(3) Next, the current switch 2 is closed (T ₂ ), the capacitor C is discharged with 32 μA, and the clock during that period is counted.

(3) When the voltage of the capacitor C exceeds 0, the comparator 7
Is detected (T ₃ ), the current switch 3 is closed via the control circuit 8 (T ₄ ), the capacitor C is charged with 1 μA, and clocks until returning to 0 are counted (T _{4 to} T ₆ ).

(4) The time interval can be measured with 10-bit resolution of the clock by calculation with the counted value of 32 μA as the upper 5 bits and the counted value of 1 μA as the lower 5 bits. Time interval Tx
When the count value of ₃₂ μA is C ₃₂ and the count value of ₁ μA is C ₁ , the arithmetic expression for obtaining is expressed by the following equation.

_{Tx = C 32/32-C} 1/1024 ... (1) < challenge invention is to solve> However, in the circuit of the above, exact ratio of three current sources 4-6 to obtain the 10 bit resolution ( Here 3
2: 1) must be adjusted. For that purpose, the ammeter 9 is connected in series with the capacitor C, and the current switches 4 to 6 are connected.
It was necessary to sequentially operate each to adjust each current value, and an additional circuit for adjustment and a connector for incorporating an ammeter were required.

The present invention has been made to solve the above problems, and an object of the present invention is to realize a time interval measuring circuit with easy current adjustment with a simple configuration.

<Means for Solving the Problem> The present invention relates to a time-expansion type time interval measuring circuit in which a plurality of different current sources are sequentially switched by current switches to charge and discharge a capacitor, and the feature is Includes a resistor connected to common, a capacitor having one end connected to common, and a current switch that selects one of the other end of the resistor and the other end of the capacitor, and the current value of the current source from the voltage across the resistor. The point is that it is configured to measure.

<Operation> When the current switch selects the resistance side, a voltage corresponding to the current value of the current source is generated at both ends of the resistance, so that the current value can be measured only by touching the both ends of the probe of the voltmeter.

<Example> Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration block diagram showing an embodiment of a time interval measuring circuit according to the present invention. The same parts as those in FIG. 2 are denoted by the same symbols. One end of the capacitor C is connected to common and the other end is connected to the positive side input terminal of the comparator 7. The negative input terminal of the comparator 7 is connected to common. One end of the constant current sources 4, 5 and 6 and one end of the resistors R1, R2 and R3 are connected to common. Current switches 11, 12, 13 are bipolar transistors or JF
It is a differential current switch composed of ET, MOSFET, etc., and by switching, the other ends of the constant current sources 4,5, 6 are respectively connected to the other end of the capacitor C or the other ends of the resistors R ₁ , R ₂ , R ₃ respectively. Connecting.
Resistors R _1, R _2, test terminals for each voltage measurement to the other end of R ₃ TP1, TP2, TP3 is connected. The output of the comparator 7 is input to the control circuit 18, and the control circuit 18 inputs a time difference input and a clock and outputs a control signal to each of the current switches 11 to 13. Here the time difference inputs determine the charging time width T ₂ -T ₁ to the capacitor C of the switch 11. The current values of the constant current sources 4, 5 and 6 and the capacitance value of the capacitor C can be the same as those in the design example of the device shown in FIG.

The operation of the circuit having the above configuration will be described below.

(1) First, the circuit is initialized. That is, by turning off both the time difference inputs, the initial state is entered after several clocks and all the current switches 11 to 13 are turned off (state in FIG. 1).

(3) Since the current of the resistor R _1, R _2, respectively R ₃ current source 4, 5, 6 is flowing, the voltage measured by voltmeter through the test terminals TP1, TP2, TP3, a current value adjust. R ₁ , R ₂ , R ₃
Assuming that the resistance value of 100Ω, 3.3KΩ, 100KΩ, the voltage appearing at the test terminals TP1, TP2, TP3 is 102.4mV, 10V, respectively.
It becomes 5.6mV and 100mV.

According to the time interval measuring circuit having such a configuration, the current value can be adjusted in a state where the initial state of the circuit is maintained, so that the additional circuit for calibration is not necessary and the cost can be reduced.

Also, since the voltage generated across both ends of the resistor can be measured and the current can be adjusted, there is no need to tamper with the circuit such as incorporating an ammeter in series with the capacitor C as in the past, and adjustment is easy because only the voltmeter probe is applied. Is. In addition, since a connector terminal for incorporating an ammeter is not required, cost can be reduced.

Also, since three voltages can be obtained at the same time, the current switch 11
It is possible to adjust at once without the need to switch from to 13 in sequence. Therefore, the adjustment is easy, the time is shortened, and the cost is further reduced.

<Advantages of Device> As described above, according to the present invention, it is possible to realize a time interval measuring circuit with easy current adjustment with a simple configuration.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a time interval measuring circuit according to the present invention, FIG. 2 is a block diagram showing a conventional example of the time interval measuring circuit, and FIG. 3 is an operation of the apparatus shown in FIG. It is a time chart shown. 4,5,6 …… Current source, 11,12,13 …… Current switch, C ……
Capacitors, R ₁ , R ₂ , R ₃ ... Resistors.

Claims (1)

[Scope of utility model registration request] 1. A time expansion type time interval measuring circuit in which a plurality of different current sources are sequentially switched by a current switch to charge and discharge a capacitor, and a resistor having one end connected to common and a capacitor having one end connected to common. And a current switch that selects one of the other end of the resistor and the other end of the capacitor, and is configured so that the current value of the current source can be measured from the voltage generated in the resistor.