JPH0451787B2 - - Google Patents

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, the transistor
Q ₁ , Q ₂ , Q ₃ , resistors R ₁ , R ₂ , R ₃ , capacitor C ₁ and constant current source I ₁ constitute a limit amplifier, transistors Q ₄ , Q ₅ , resistors R ₄ , R ₅ , constant current Source I ₂ ,
I ₃ constitutes an electric field detection circuit.

The intermediate frequency signal input to the base of transistor _Q1 is amplified by a limiter amplifier and output to the emitter of transistor _Q3 . Capacitor C ₁
Assuming that the impedance of is sufficiently small with respect to the signal frequency (1/wc ₁ ≈0), the base potential of the transistor Q ₅ is kept at a constant DC potential. On the other hand, since the base potential of transistor _Q4 changes according to the signal output of transistor _Q3 , half-wave electric field detection is performed by transistors _Q4 and _Q5 , and electric field detection output current flows to transistor _Q4 . The resistor R ₄ and the constant current source I ₂ are a level shift circuit, which lowers the base potential of the transistor Q ₄ by the base potential of the transistor Q ₅ and prevents current from flowing to the transistor Q ₄ when no signal is input. do.

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

(Problems to be Solved by the Invention) 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 a minute signal is input, causing an offset. There was a drawback that caused this. Furthermore, this offset component has a positive temperature coefficient, causing temperature characteristics in the electric field detection characteristics, and this 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 detected by the electric field decreases. The component becomes small and affects the 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 causing the current to flow, the occurrence of offset is prevented without particularly lowering the base potential of 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.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of the present invention. 1 is the output signal of the limiter amplifier, which is the output signal of the limiter amplifier shown in FIG. 2, Q ₆ is the third transistor, R ₇ is the resistor, and I ₄ is the constant current source. Components with the same functions as those in FIG. 2 are given the same reference numerals.

The difference from the conventional technology is the addition of transistor _Q6 . The base of transistor Q ₆ is
It is commonly connected to the base of the transistor _Q5 , and is always at a constant potential Vs, its collector is connected to the power supply _VD , and its 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.

When there is no signal, the base potential of transistor Q ₆ is Vs, and the base potential of transistor Q ₄ is lower than Vs by the amount of level shift, so the resistor
The current flowing through R ₇ becomes the current flowing through transistor Q ₆ instead of transistor Q ₄ .

In this way, this circuit allows current to flow from transistor Q ₆ when there is no signal, thereby causing current to flow from transistor Q ₄
It is constructed to prevent offset by not allowing current to flow through the capacitor. Needless to say, such a circuit also includes IC implementation.

(Effects of the Invention) As explained above, the present invention eliminates the offset when there is no signal or when a small signal is input by adding the third transistor, and eliminates the need for a complicated offset correction circuit. It is possible to achieve excellent temperature characteristics in terms of electric field detection characteristics. Especially when making multi-stage connections,
There is an advantage that a circuit having a wide range electric field detection function that is less affected by temperature can be obtained.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a circuit diagram of a conventional example. 1... Limiter amplifier output signal, Q ₄ ... 1st
transistor, Q ₅ ...second transistor,
Q ₆ ... third transistor, R ₄ , R ₇ ... resistance,
C ₁ ... Capacitor, I ₂ , I ₄ ... Constant current source.

Claims (1)

[Claims] 1 Connect a resistor between the emitters of a pair of transistors consisting of the first and second transistors, apply a high frequency signal to the base of the first electric field detection output transistor, and maintain the base of the second transistor at a constant potential. In a circuit for electric field detection, a third transistor whose collector and base are respectively connected to the collector and base of the second transistor and whose emitter is connected to the emitter of the first transistor is provided.
An electric field characterized in that the third transistor is provided with a transistor, and the offset current generated in the first transistor when there is no signal or a small signal is made zero by replacing it with a third transistor, thereby preventing the influence of the offset on electric field detection. detection circuit.