JPH01126566A - Electric field detection circuit - Google Patents

Abstract

PURPOSE:To omit a complicate offset correction circuit while realizing excellent temperature characteristic in an electric field detection characteristic, by adding a third transistor (Tr) to an electric field detection circuit 10 let a first offset current to the Tr as replacement. CONSTITUTION:A resistance R7 is connected between emitters of a pair of transistors Tr comprising first and second Trs Q4 and Q5, a high frequency signal is applied to the base of the TrQ4 for a first electric field detection output to perform a detection of an electric field by maintaining the base of the second TrQ5 at a fixed potential. Circuits thus obtained are provided with a third TrQ6 to have the collector and base thereof connected to the collector and base of the TrQ5 respectively while the emitter thereof is connected to the emitter of the TrQ4. Then, an offset current generated with the TrQ4 in the absence of a signal or in the presence of a microsignal is down to zero by replacement with the TrQ6, thereby preventing effect of offset in the detection of an electric field.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric field detection circuit for a receiver used in mobile radio and the like.

(Prior Art) FIG. 2 shows a circuit diagram of a conventional intermediate frequency amplifier and electric field detection circuit. In the same figure, transistors Q, ,Q,,Q
,, resistors R1, RI R3, capacitor C1, and constant current source I constitute a limiter amplifier, and transistor Q
-, Q6, resistors R, , R5, and constant current sources 1y and Is constitute an electric field detection circuit.

A first-year junior high school student who was made into the base of transistor Q? The f1 frequency signal is amplified by a limiter amplifier, and the transistor Q,
is output to the emitter of Assuming that the impedance of capacitor C3 is sufficiently small relative to the signal frequency, (1/
w c , hand 0), the base potential of the transistor Q5 is kept at a constant DC potential. - side, transistor Q4
Since the base potential of transistor Q3 changes according to the signal output of transistor Q3, half-wave electric field detection is performed by transistors Q4 and Q, and electric field detection output current flows to transistor Q4. A constant current source (2) with a resistor R is a level shift circuit that lowers the base potential of the transistor Q4 below the base potential of the transistor Q5, thereby preventing current from flowing through the transistor Q4 when no signal is input.

These intermediate frequency amplifiers and electric field detection circuits are connected in multiple stages to perform electric field detection in a sequential manner.

(The interlude that the invention seeks to solve) In the conventional electric field detection circuit, if the amount of level shift (DC) is inappropriate, a minute DC current flows through the transistor Q4 when there is no signal or when a minute signal is input, causing an offset. There was a drawback that caused Furthermore, this offset component has a positive temperature coefficient, causing temperature characteristics in the electric field detection characteristics, and the effect is particularly large in the case of multi-stage connections.

On the other hand, as the amount of level shift increases, the base potential of transistor Q4 decreases, and the offset current flowing through transistor Q4 can be made smaller. However, if the amount of level shift is too large, the signal component that cannot be detected by the electric field will decrease. It becomes small,
Affects electric field detection characteristics.

Furthermore, if the limiter operates at a low voltage, the magnitude of the output amplitude of the limiter is limited, so naturally the amount of level shift cannot be increased, and the occurrence of offset cannot be prevented.

(Means for Solving the Problem) Based on this background, the present invention adds a third transistor to the conventional electric field detection circuit, and uses this transistor to replace the offset current of the first transistor Q4. By allowing the current to flow, the occurrence of offset is prevented without particularly lowering the base potential of the transistor Q4, and the electric field detection characteristics are improved. Embodiments of the present invention will be described in detail below with reference to the drawings.

(Example) FIG. 1 is a circuit diagram showing an embodiment of the present invention.

l is the output signal of the limiter amplifier shown in Fig. 2, Q is the third transistor, R7
is a resistor, and 4 is a constant current source.

Components with the same functions as those in FIG. 2 are given the same reference numerals.

The difference from the prior art is that a transistor Qll is added. The base of the transistor Q6 is connected in common with the base of the transistor Q, and is always at a constant potential Vs, the collector is connected to the power supply Vo, and the emitter is connected to the resistor R7, which together with the emitter of the transistor Q4 determines the magnitude of the electric field detection output current. ing.

When there is no signal, the base potential of the transistor Q6 is Vs, and the base of the transistor Q4 is at a potential lower than Vs by the amount of level shift, so the current flowing through the resistor R7 is the current flowing through the transistor Q, not through the transistor Q4. .

In this way, this circuit converts the current during no signal to the transistor Q
, thereby preventing current from flowing through the transistor Q4 and preventing offset. It goes without saying that such a circuit also includes IC implementation.

(Effects of the Invention) As explained below, the present invention is designed to remove the offset when there is no signal or when a small signal is input by adding the third transistor, and the present invention eliminates the need for a complicated offset correction circuit. can be omitted, and excellent temperature characteristics can be realized in terms of electric field detection characteristics. Particularly when multi-stage connections are made, there is an advantage that a circuit having a wide range of electric field detection functions that is less affected by temperature can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional example. ■...Limiter amplifier output signal, Q4...first transistor, Qs...second transistor, Q6...
・Third transistor, R,, R9...Resistance, CI・
...Capacitor, I,,1. ...constant current source. Patent applicant Japan Radio Co., Ltd.

Claims (1)

[Claims] A resistor is connected between the emitters of a pair of transistors consisting of the first and second transistors, a high frequency signal is applied to the base of the first electric field detection output transistor, and the base of the second transistor is maintained at a constant potential. In a circuit that detects an electric field, a third transistor is provided whose collector and base are connected to the collector and base of the second transistor, respectively, and whose emitter is connected to the emitter of the first transistor, and when there is no signal or a small signal, An electric field detection circuit characterized in that the offset current that sometimes occurs in the first transistor is replaced by a third transistor to make it zero, thereby preventing the influence of the offset on electric field detection.