JPH018007Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a circuit that converts current into voltage.
The present invention relates to a current-voltage conversion circuit that suppresses spike noise generated when switching a feedback resistor.

FIG. 1 is a block diagram of a current-to-voltage conversion circuit with a conventional resistor switching circuit. This circuit is a well-known circuit in which a current I flowing through a test element 3 connected between input terminals 1 and 2 is passed through a high gain amplifier 4.
The voltage is converted by a feedback resistor 5 etc. connected between the input and output terminals of the circuit, and a voltage V _A proportional to the current is derived from the output terminal 12. Here, the feedback resistor is normally switched depending on the magnitude of the current flowing through the test element 3. This switching is performed by turning on and off a switch (reed relay) 7. However, at the moment when the switch 7 is turned on, for example, the response speed of the amplifier 4 is finite, so it cannot respond instantaneously to this resistance change, and the output voltage V _A remains constant. , input voltage V _B ).
This spike noise usually reaches several volts, and when a semiconductor element is connected as the test element 3, it has an adverse effect such as changing the measurement conditions.

Therefore, the present invention has been made to eliminate the above-mentioned drawbacks, and the object of the present invention is to provide a current-to-voltage conversion circuit that can suppress spike noise generated when switching a feedback resistor.

FIG. 2 is a block diagram of a current-to-voltage conversion circuit with a resistor switching circuit according to an embodiment of the present invention. The same parts as in FIG. 1 are given the same reference numerals. Only the parts that are different from FIG. 1 will be explained. amplifier 4
A series circuit consisting of switch 7 and feedback resistors 9 and 11 is connected between the input and output terminals of . And a junction type between the connection point of resistors 9 and 11 and the reference potential point.
A semiconductor switch 19 such as a FET, MOSFET, or bipolar transistor is connected. 15,17
are a switch control circuit and a sawtooth signal generator, respectively, which generate signals V _Q and V _G in response to a control signal V _P applied to terminal 13, respectively. signal
V _Q to switch 7, signal V _G to semiconductor switch 1
9 control terminals, respectively. Note that the switch 7 is for completely turning off the feedback circuit including the resistors 9 and 11, and is not an essential requirement.

The operation will be explained below. FIG. 3 shows two configurations made depending on the size of the feedback resistor (range resistor) and their equivalent circuits during various operations. FIG. 4 is a waveform chart showing the operation of each part. Below is the semiconductor switch 19 as N channel.
The case will be explained separately as a FET.

Case a in Figure 3 This configuration is the same as the configuration in Figure 2, but parts that are unnecessary in principle have been omitted. R _R1 indicates a series composite resistor of resistors 9 and 11, and ON means that this composite resistor is connected in parallel to resistor 5, and the feedback resistance value is approximately determined by the resistance value of this series composite resistor. , and off means that they are not equivalently connected in parallel. This configuration has R ₅ = 100MΩ, R ₉ =
Used when switching high resistances such as 990KΩ and R ₁₁ = 10KΩ. First, the feedback resistance value is approximately R ₉ + R ₁₁ =
We will explain the case of switching the feedback resistor to 1MΩ (parallel connection). The equivalent circuit in this case is shown in FIG. 3b. Please refer to FIG. The signal V _P changes from an ON signal to an OFF signal, and the signal
V _G is a constant slew from maximum to maximum.
Changes in rate (slew rate, slope, voltage/time). When V _G falls to a certain value, the FET 19 slowly changes from on to off. That is, FET1
The resistance value (R _F ) between the drain and source of No. 9 changes slowly. At some point when V _G has fallen further, FET
19 is completely turned off. V _Q changes like V _Q1 . Here, one terminal of FET19 and resistor 1
The voltage at the node s of 1 is the output voltage V _A with R ₁₁
The voltage divided by R _FOFF is V _S ≒ V _A. R ₅ ≫ (R ₉ + R ₁₁ )
Therefore, the input current I flows through the resistors 9 and 11, and the feedback resistance value is approximately determined by R ₉ +R ₁₁ , which means that the feedback resistor has been switched. As is clear from the above explanation, the resistance value of the FET 19 is switched slowly, and the amplifier 4 can follow that speed. In other words, since the slew rate of the amplifier 4 is greater than the slew rate of V _G , the resistance value of the FET 19 is switched slowly. No spike noise occurs in _B.

Next, a case will be described in which the feedback resistor is switched so that the feedback resistance value is determined only by _R5 . The equivalent circuit in this case is shown in FIG. 3C. When V _P turns from on to off, simultaneously or with a slight delay, the signal V _G changes from maximum to maximum at a constant slew rate. That is, FET19
change from on to off. When V _G reaches a certain value, FET 19 begins to turn on and its resistance value is slowly changed. FET 19 then turns completely on. In this case, V _S ≈0V, and the input current I flows through the feedback resistor 5, which is determined only by the resistor 5. In this case as well, since the source-drain resistance value of FET 19 changes slowly, no spike noise is generated at _VB . Note that since FET 19 must be turned on and off while relay 7 is on, V _Q1 is turned off after FET 19 is turned on. That is, the control circuit 15 includes a delay circuit, and after V _P is turned on, V _Q1 is turned off after a delay time.

Case d in Figure 3 This configuration differs from the case in Figure 3 a, in that the FET 20 is connected in series with the resistor 9, and the resistor 13 is connected between the connection point s of the resistor 9 and FET 20 and the reference potential point. is connected. This configuration has R ₅ = 10KΩ,
Used for low resistance switching such as R ₉ = 75Ω and R ₁₃ = 10KΩ. First, the feedback resistance value is approximately R ₉ + R _FON
We will explain the case of switching the feedback resistor so that = 100Ω (parallel connection). The equivalent circuit in this case is shown in FIG. 3e. Change FET20 from off to on. When V _G reaches a certain value, FET 20 begins to turn on and its resistance value changes slowly. When FET20 is completely turned on, V _S ≒ V _A , and the feedback resistance value is approximately R ₉ +
Determined by R _FON . V _Q changes like V _Q2 .

In the case of f in FIG. 3, the FET 20 is controlled to be turned off, and the feedback resistance value is approximately determined by _R5 .
Depending on the range resistance value, a and d in Figure 3.
The reason for distinguishing the configurations is that if, for example, f in FIG. 3 were to have the same configuration as c, it would not be possible to make V _S ≈0V since R _FON would have a considerable value.

As is clear from the above explanation, according to the present invention, the spike noise generated when switching the feedback resistor is suppressed, and even if a semiconductor element is connected as the test element 3, the characteristics measurement thereof will not be adversely affected. The present invention is extremely effective when used in a device that converts a current flowing through a semiconductor element into a voltage and detects the current.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a current-to-voltage conversion circuit equipped with a conventional resistor switching circuit, and FIG. 2 is a block diagram of a current-to-voltage conversion circuit equipped with a resistor switching circuit according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram of the operation of the present invention including other embodiments of the present invention, and FIG. 4 is a waveform diagram of each part of the present invention. 3: Test element, 7: Switch, 15: Switch control circuit, 17: Sawtooth signal generator, 19: Semiconductor switch.

Claims (1)

[Scope of utility model registration request] Connect a feedback resistor between the input and output terminals of the amplifier,
In the circuit that converts the input current to the amplifier into voltage, resistors and resistors (or semiconductor switches)
and a semiconductor switch (or resistor) connected between the connection point of the resistor and the resistor (or semiconductor switch) and a reference potential point;
a resistor switching circuit comprising a sawtooth signal generator connected to a control terminal of the semiconductor switch, connected between input and output terminals of the amplifier such that the series circuit is connected in parallel to the feedback resistor; A resistor switching circuit configured to substantially switch the feedback resistance value between the input and output terminals of the amplifier to the resistance value of the feedback resistor or the series circuit in response to the on/off operation of the semiconductor switch. Current-voltage conversion circuit.