JPS5923494B2 - Slope signal generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a slope signal generation circuit for an oscilloscope, etc.
In particular, it is an object of the present invention to provide a slope signal generation circuit that can electronically switch a constant current over a wide range and with a simple circuit configuration.

A generally known slope signal generation circuit for an oscilloscope is configured as shown in FIG. 1, for example.

R1-R8 are timing resistors, C1-C8 are timing capacitors, and the timing resistor selected by the selector switch S1 and the common base type constant current drive transistor Q1
A constant current source is constructed from the above, and the constant current charges the timing capacitor selected by the selector switch S2 and generates a ramp signal.

The slope of the slope signal is selected over a wide range by the combination of timing resistors R1-R8 and timing capacitors C1-C8.

Usually, a mechanical switch such as a low-pressure switch is used as this changeover switch.

Here, 1 is a timing pulse input terminal, and 2 is an impedance conversion circuit that outputs a slope signal at low impedance.

3 is an output terminal that outputs a slope signal with low impedance.

The above is an example of obtaining a slope signal by selecting a wide range of slopes using a mechanical switch. However, if this slope is selected by an electrical signal, such as the output of a logic circuit, or by remote control, a mechanical switch is used. A circuit as shown in FIG. 2 can be used without using a switch.

When a logic signal is applied to the terminals P11 to P18 and terminals P21 to P2g to turn on any of the transistors Q21 to Q28 and turn off any of the transistors Q1□ to Q18, the corresponding common base type constant is activated. One of the current drive transistors Q1 to Q8 is turned on,
The desired constant current and timing capacitors are selected.

Normally, in an oscilloscope, there are 6 to 8 timing resistors to choose from, so the number of parts increases and the circuit becomes complicated, as shown in FIG.

Further, considering the dynamic range of the constant current source, the base potential of the constant current driving transistors Q1 to Q8 must be set sufficiently high.

Therefore, it is difficult to control whether or not current flows through these transistors Q1 to Q8 directly at the logic circuit level.

Transistors Q1□ to Q18 are level conversion circuits for this purpose.

However, if an open collector with high voltage resistance is used in the output stage of the logic circuit, this level conversion circuit can be omitted.

However, even when using this open collector logic circuit element, eight timing resistors R1 to
Many parts and mounting space are required to switch R8.

In order to eliminate these drawbacks, the present invention eliminates the need for mechanical switches, level conversion circuits, and constant current drive transistors equal to the number of timing resistors to switch timing resistors, and allows constant current to be easily and easily controlled over a wide range. The present invention provides a slope signal generating circuit that can be electronically switched with a circuit configuration, and will be described in detail below with reference to the drawings.

FIG. 3 shows an embodiment of the present invention.

In the figure, parts having the same functions as those in FIGS. 1 and 2 are given the same reference numerals.

The timing resistors R1 to R8 are connected to the collectors of the switching transistors Qll to Q18 whose emitters are grounded, respectively, and the other ends are connected to a constant current drive transistor Q5□ of a grounded base type.

The emitter potential of this transistor Q51 is
The base potential of the transistor Q5□ is maintained at a potential approximately 0.6 volt lower than the base potential determined by the division of the transistor Q5□.

When any one of the terminals pH to P18 is set to a high level by the output of a logic circuit (not shown), any one of the corresponding transistors Q11 to Q12 becomes conductive and saturates at the same time, causing the timing resistors R1 to R8 to become high level. Voltage is applied to one of them and current flows.

This current is made constant by transistor Q51 and resistor R5
It flows to 2.

This generates a voltage across the resistor R5□, and the same voltage is applied to the resistor R by a current mirror circuit composed of an operational amplifier A1 and a constant current drive transistor Q1.
The current that appears at both ends of the resistor R5□ passes through the constant current drive transistor Q1, and is connected to the terminals P2□ to P28.
The output of a logic circuit (not shown) applied to the output signal flows to a timing capacitor connected to the transistor in which one of transistors Q21 to Q28 is turned on.

Here, by setting the resistors R52 and R51 to the same resistance value, the same constant current as the constant current generated by the transistor Q51 can flow through the transistor Q1.

In this way, a constant current corresponding to the timing resistors R1 to R8 can be caused to flow through the transistor Q1 by the current mirror circuit.

By the way, in an oscilloscope, it is usually necessary to switch the constant current value over a wide range, for example, from 10 μA to 5 mA, so it is difficult to cover everything with only the resistors R5□l and R5□.

This is because in order to accurately transfer current from transistor Q51 to transistor Q1, resistor R5 is required even when the current is small.
11R52 must generate such a voltage that the input offset voltage of the operational amplifier A1 can be ignored.

If the current increases, a very large voltage will be applied to the resistors R51JR52, so it is necessary to change their resistance values according to the current.

Constant voltage diode D51 t D52 and resistor R,, R
, t R55°R56 is for this purpose, and is a circuit whose resistance is switched according to the current.

At this time, the resistors R53 and R54 and the resistors R55 and R56 need to have the same resistance value.

The current is small and the resistance R5□. When the voltage across R5□ is smaller than the constant voltage value of the constant voltage diode D51, D51 is off and the current is detected by the resistors R51° and R52.

When the current increases and the voltage across resistors R51 and R32 exceeds the constant voltage value of the constant voltage diode D51, D51 turns on and the current flows through the parallel circuit of resistors R5□ and R53 and the resistor R5.
2 and R54 in parallel circuit.

Similarly, when the current increases further, the voltage regulator diode D5□
is also turned on, and the current flows through the resistor R51 + R53t R55
parallel circuit and resistor R5□.

It is detected by the parallel circuit of R541R56.

As described above, the present invention can provide a ramp signal generation circuit that can electronically switch current values over a wide range and with a simple circuit configuration without using a mechanical switch or a level conversion circuit for constant current switching.

It goes without saying that the present invention is applicable not only to oscilloscopes but also to other devices having constant current circuits that switch and use constant current.

[Brief explanation of drawings]

Figure 1 shows a typical oscilloscope slope signal generation circuit, Figure 2 shows a conventional electronically switchable slope signal generation circuit,
FIG. 3 shows an embodiment of the present invention, where R1-R8 are timing resistors, 01-C8 are timing capacitors, and Q51
t Ql is a constant current drive transistor, D51 e
D5□ is a constant voltage diode, and A1 is an operational amplifier.

Claims (1)

[Claims] 1 a first constant current drive element, a plurality of timing resistors each having one end connected to the second constant current drive element, a plurality of switching means each connected to the other end of the timing resistor, one end of which is connected to the second constant current drive element; A first impedance element connected to a power supply and whose other end is connected to the output of the first constant current drive element to detect the output current thereof, and the impedance of the first impedance element have an impedance that is equal to the impedance of the first impedance element. a second impedance element having one end connected to a power supply;
The other end of the first impedance element and the other end of the second impedance element are input, and a voltage equal to the voltage generated in the first impedance element is generated in the second impedance element. an operational amplifier having a second constant current drive element connected to its output that outputs a current equal to the current flowing through the constant current drive element;
A ramp signal generation circuit comprising a timing capacitor connected to a constant current drive element.