JPH0339927Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an electric field received signal strength 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 ₁ , Q ₂ , Q ₃ , resistors R ₁ , R ₂ , R ₃ , R ₄ , capacitor C ₁ and constant current source I ₁ constitute an intermediate frequency amplifier, and transistors Q ₄ , Q ₅ , resistor R ₅ , constant current source
I ₂ and I ₃ constitute an electric field detection circuit.

The intermediate frequency signal input to the base of transistor _Q1 is amplified by an intermediate frequency amplifier and output to the emitter of transistor _Q3 . capacitor
Assuming that the impedance of C ₁ is sufficiently small relative to the signal frequency (1/WC ₁ ≒O), the transistor
The base potential of Q ₄ is kept at a constant DC potential.
On the other hand, since the base potential of transistor _Q5 changes according to the signal output of transistor _Q3 , half-wave electric field detection is performed by transistors _Q4 and _Q5 ,
The electric field detection output current flows through transistor _Q4 .
Resistor R ₂ and constant current source I ₂ are level shift circuits,
Transistor Q ₄ base potential to transistor Q ₅
It works to prevent current from flowing to 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.

(Problem that the invention aims to solve) In conventional electric field detection circuits, if the amount of level shift (DC) is inappropriate, a small amount of direct current flows through transistor _Q4 when there is no signal or a small 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 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 Problems) Based on this background, the present invention connects a resistor between the emitters of a pair of transistors consisting of a first transistor and a second transistor, and Adding a high frequency signal to the base, level-shifting the DC potential on which the high frequency signal is superimposed and applying it to the capacitor, a constant potential obtained is added to the base of the first transistor, and as a third transistor,
The emitter is connected to the emitter of the first transistor, and the collector and base are respectively connected to the emitter of the first transistor.
connected to the collector and base of the transistor,
The third transistor is provided to substitute the offset current generated when there is no signal or a small signal by applying the unlevel-shifted potential to the base, and the third transistor is connected to the first transistor. By flowing instead of the offset current of the transistor _Q4 , 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.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of the present invention. Components having the same functions as those in FIG. 2 are given the same reference numerals. _Q6 is the third transistor. The difference from the conventional technology is the transistor _Q6
, the base of transistor Q ₆ is commonly connected with the base of transistor Q ₅ , and the base potential changes according to the signal output of transistor Q ₃ ,
The collector is connected to the power supply V _D , and the emitter is a transistor.
Together with the emitter of _Q4 , it is connected to a resistor _R5 that determines the magnitude of the electric field detection output current.

When there is no signal, the base potential of transistor _Q6 is V _P
Then, the base of transistor _Q4 is at a potential lower than V _P by the amount of level shift, so the resistor
The current flowing through _R5 becomes the current flowing through transistor _Q6 instead of through transistor _Q4 .

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 includes IC implementation.

(Effects of the invention) As explained above, the 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;
The figure is a circuit diagram of a conventional example. _Q4 ...first transistor, _Q5 ...second transistor, _Q6 ...third transistor, _R1 ,
_R2 ...Resistor, _C1 ...Capacitor, _I1 ...Constant current source.

Claims (1)

[Scope of utility model registration request] A resistor is connected between the emitters of a pair of transistors consisting of a first and a second transistor, and the second
A high-frequency signal is applied to the base of the first transistor, and a constant potential obtained by level-shifting the DC potential on which the high-frequency signal is superimposed and applied to the capacitor is applied to the base of the first transistor, and as a third transistor, the emitter is By connecting the emitter of the first transistor, connecting the collector and base to the collector and base of the second transistor, and applying the non-level shifted potential to the base, it is possible to An electric field detection circuit characterized in that the third transistor is provided to substitute the generated offset current so that the electric field detection by the first transistor is not affected by the offset.