JPS60209186A - Voltage detecting circuit - Google Patents

Abstract

PURPOSE:To detect the difference between electric signals with optional voltages by applying signals to be compared to the base and emitter of a transistor Tr, and leading out the collector output of the Tr through a current mirror circuit. CONSTITUTION:The signals to be compared are supplied to detection terminals (a) and (b), the terminal (b) is connected to the base of the Tr Q1 through a diode D1 for level shifting, and the base of the Tr Q1 is biased by a constant current source (e). The terminal (a), on the other hand, is connected to the emitter of the Tr Q1 through a resistance R1, the collector output of the TrQ1 is applied to the current mirror circuit of a diode D3 and a Tr Q3 through the current mirror circuit of a diode D2 and a Tr Q2, and a resistance R2 is regarded as a load to obtain an output Vd at an output terminal (d). Further, a constant current source (f) is set equal to the current flowing through the Tr Q1 when the voltage between both terminals (a) and (b) is zero. Therefore, this detecting circuit detects the difference voltage between two signals with optional voltages without reference to the voltage at a power terminal (c).

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a voltage detection circuit, and is particularly suitable for integration into an integrated circuit.

(Prior art) Most conventional detection circuits use power supply voltage to drive a power supply circuit that receives electrical signals to be compared.

If the electrical signal to be compared was higher than the power supply voltage, comparison could no longer be detected.

(Object of the Invention) An object of the present invention is to provide a voltage detection circuit that can detect a difference between electrical signals having arbitrary voltages.

(Structure of the Invention) According to the present invention, a voltage detection circuit is obtained in which a signal to be compared is applied to the pace and emitter of a transistor, and the collector output of this transistor is extracted by a current mirror circuit.

(Example of the invention) The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. A and b are detection terminals, and signals to be compared are given to each detection terminal a and b. ○C is a power supply terminal, and d is an output terminal. The detection terminal S is connected to the base of the transistor Q1 through a level shifting diode D. The base of transistor Q1 is biased by constant current source 1. The detection terminal (a) is connected to the transistor Q1 via the resistor R1.
is connected to the emitter of The output from the collector of transistor Q is applied to the current mirror circuit of diode D3 and transistor Q3 via the current mirror circuit of diode D2 and transistor Q2, and the output Vd is taken from output terminal d with resistor L as a load. It's being served. The constant current source 2 is set to be equal to the current flowing through the transistor Q1 when the voltage between the rain detection terminals a and b is zero.

Now, if the voltage between rain detection terminals a and b is vs, the diode D1. The following relationship holds true between transistor Q1 and resistor R1.

vS tenv, □=:=IQ0. R1+VBB□ ・Old・・
...(1) However, VFI: diode DlQ forward voltage VBE □ Nido 2 transistor Qt base-emitter voltage: Boltzmann constant T: absolute temperature q: electron charge I8D: saturation current of diode DI ■8Q: Saturation current I8 of transistor q: Current Iqx of constant current source 1:) Emitter current of transistor Qt
The emitter current of transistor Q1 is IQI=(V8+
ΔVBB)/R□ ・・・・・・・・・(4) 〇Otherwise, the voltage Vd of the output terminal d is the voltage Vd of the transistor Q1
．． Q2. When the current amplification factor of Qa is large, the base current can be ignored, and the following equation is obtained.

Va= (IQ, -I2)・Crow ・・・・・・・・・
(6) 2: Current of constant current source 2 Here, I2 is set equal to the current when vs = 00, and according to equations (4) and (5), I2 = ΔVBF, @A, ・・・・・・・・・・(7) However, ΔVBE(0):ΔVBEIQI( when VS:O
0): Expressed as Q1 when VS=0.

In this way, from Equations 1 (4) to (8), the voltage V at output terminal d
d is V(1=(VB+ΔVBE−ΔVnn(o))4'Lz
/ILI-”('1■d:8:■5-R2/R,1・
・・Shouts・・(Foundation) Tonashi, output terminal d has rain detection terminal a
, b generates a voltage Vd that is approximately proportional to the voltage difference between 5 and 5. By the way, the detection terminal a receives the voltage to be compared.

b is connected to the base and emitter of the transistor Q1, and is separated from the power supply terminal C of the circuit.

Therefore, this detection circuit can detect the difference voltage between two signals having arbitrary voltages, regardless of the voltage at the power supply terminal C. That is, it is possible to detect a voltage difference between signals having a higher voltage than the power supply voltage.

Next, FIG. 2 shows another embodiment of the present invention. In this embodiment, in addition to the embodiment shown in FIG. 1, a resistor 3. R4゜R,,R
6 is added to suppress the offset between the diode and transistor that constitute the current mirror circuit.

The resistor R8 between the rain detection terminals a and b is a resistor for current detection, and is not necessary when directly comparing voltages. Note that elements and terminals with the same symbols as in FIG. 1 indicate the same items.

In the embodiment shown in FIG. 2, the relationship between the voltage vs between the rain detection terminals a and b and the voltage vd at the output terminal d is the same as in the embodiment shown in FIG. The resistor R8 allows the current value to be detected. Namely.

For the current ■o flowing through the resistor S, ■, = 几, · 0 ・・・・・・・・・・・・(B) Therefore, according to equations (6) and (6), Vd Medium engineering 0/R5
-R2/R, □ ・・・・・・・・・At 0, the current flow o is detected isometrically.

Next, FIG. 3 shows yet another embodiment. Also in FIG. 3, elements and terminals having the same symbols as those in FIG. 2 indicate the same elements. The difference is that NPN is used instead of diode D1.
The reason is that the area between the base and emitter of transistor Q4 is used. As is well known, since the forward voltage of a diode and the base-emitter voltage of a transistor are very similar, it is clear that the example shown in FIG. 3 can also obtain characteristics similar to those shown in FIG. 2. Furthermore, in the embodiment shown in FIG. 2, the current 1 of the constant current source 1 is included as is as the current ■o flowing through the current detection resistor R8, whereas in the embodiment shown in FIG. This method has the effect that only the current is included, and is particularly effective for circuits with a small amount of current.

As described above, according to the present invention, it is possible to realize a voltage detection circuit that can detect a difference between any two voltages and obtain a voltage proportional to this difference, regardless of the power supply voltage that drives the detection circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of a voltage detection circuit according to the present invention, FIG. 2 is a circuit diagram showing another embodiment according to the present invention,
FIG. 3 is a circuit diagram showing yet another embodiment.

Claims (1)

[Claims] 1) first and second terminals receiving signals to be compared;
An emitter is connected to the first terminal. a transistor whose base is connected to the second terminal;
A voltage detection circuit comprising: a current mirror circuit having an input section connected to the collector of the transistor; and means for extracting an output from the current mirror circuit. 2) the current mirror circuit includes a first diode connected between the collector of the transistor and ground potential;
a second transistor connected between the pace and the emitter in parallel to the first diode; a second diode connected between the collector of the m2 transistor and the power supply terminal; and a base and emitter connected to the second diode. 2. The voltage detection circuit according to claim 1, further comprising a third transistor having three transmitters connected in parallel.