JPS61170104A - Intermediate frequency amplifier circuit - Google Patents

Abstract

PURPOSE:To form a circuit having an electric field detecting function with excellent linearity of an electric field detection voltage and temperature characteristic by constituting the circuit with an AGC circuit comprising multi-stage AGC amplifiers and using an AGC control voltage when the output voltage of the final stage is constant so as to detect the input electric field level of an intermediate frequency amplifier circuit. CONSTITUTION:n-Stages of AGC amplifies are provided, an output of each stage is connected to an input of the next stage, and an AGC control voltage is impressed from an AGC control voltage generator 2 to all the AGC amplifiers of the n-stage in common so that the output of the AGC amplifier of the n-th stage. Then the said AGC control voltage has a pseudo logarithmic characteristic to the input voltage of the 1st AGC amplifier. The output voltage Vo is controlled by the AGC control circuit 2 so that output voltage Vo is constant after it is rectified by a capacitor Crec with a load RL connected to the n-th stage of the output section. Thus, the pseudo logarithmic characteristic with excellent linearity is obtained over a wide range. Thus, the input electric field level to the intermediate frequency amplifier is detected by the AGC control voltage and the pseudo logarithmic characteristic with excellent linearity is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the configuration of an intermediate frequency amplifier of a receiver, and in particular to a method of detecting a received electric field of a receiver suitable for use in mobile radio, telemeters, etc. It is.

Prior art Prior art to the present invention includes, for example, ゛, Micro-
electronics and
ty, vol, 16, PP, 45-3
66, Pergamon Press, 1977
exists. The circuit configuration of FIG. 3, which is disclosed as a conventional example of the present invention, is the OA 308 shown in the above-mentioned document.
This is an extracted part of IC No. 9. Other parts in the above document that are related to FIG. 3 of this specification are F”
igl.

Fig2, Fig10, Fig11,
Fig. 12 and its explanatory text.

Conventionally, the configuration of an intermediate frequency amplifier having this type of electric field detection function is as shown in FIG.
2nd stage transistor Q20 consisting of 11' to Q19'
The output of each stage (3rd stage consisting of '~Q27') is rectified via capacitors (G8', 09', (310'), and the rectified voltages of each stage are added to output electric field level information. was.

Problems to be Solved by the Invention However, it is often seen that the linearity of the sum of the rectified voltages of each stage deteriorates, and as shown in FIG. 4, unevenness appears in the electric field detection voltage.

Also, the signal current flows through diodes (Q28', Q29
'.

Q30' IQ32, Q33, Q34 + Q
35', Q36', Q37'), the disadvantage is that the temperature characteristics are particularly poor and the circuit becomes complex to compensate for the temperature characteristics.

In fact, each rectifier has a capacitor (08', 09'
.

Therefore, if the intermediate frequency is lowered, a large capacitor is required, and the intermediate frequency of the IC is generally 10.7 MHz. In this case, if the intermediate frequency was lowered, it would be difficult to incorporate the compensator, and a terminal for the external capacitor for the rectifier would be required for each stage, which was disadvantageous for IC implementation. Furthermore, if the intermediate frequency is raised, it is difficult to achieve amplification unless current is passed through each stage of amplifier, making it difficult to reduce current consumption.

The present invention has been made in order to improve the above-mentioned drawbacks inherent in the conventional technology, and therefore, an object of the present invention is to have excellent linearity and temperature characteristics of electric field detection voltage, operate with low current, and The object of the present invention is to provide a novel intermediate frequency amplification circuit having an electric field detection function with fewer parts.

Means for Solving the Problems In order to achieve the above object, the intermediate frequency amplification circuit according to the present invention includes a first pair of transistors in which the respective emitters of the first pair of transistors are connected in common through respective resistors. a differential amplifier; a second differential amplifier in which the emitters of each of the second pair of transistors are commonly connected to the collector of one of the first pair of transistors via a resistor; a third differential amplifier in which the respective emitters of the third pair of transistors are commonly connected to the collectors of the other transistors of the first pair of transistors through respective resistors; It has n stages of AGC amplifiers each consisting of a resistor connected to the collectors of the second and third pair of transistors so that the outputs of the dynamic amplifiers are opposite to each other, and the output of the first stage AGC amplifier is Connected to the input of the second stage AGC amplifier,
Sequentially, the output of the (n-1) stage AGC amplifier is connected to the input of the n-th stage ACTO amplifier, and the n-th stage AGC amplifier is connected to the input of the n-th stage ACTO amplifier.
In order to keep the output of the amplifier constant, a common ACTO control voltage was applied to all n-stage AGC amplifiers from the first stage AG (j amplifier to the n-th stage AGC amplifier switch). In the AGC circuit, the first stage A('TC
The AGC control voltage of the AGC circuit has a pseudo-logarithmic characteristic with respect to the input voltage of the amplifier.

Principle of the Invention The principle of the present invention is that the intermediate frequency amplifier circuit is configured with an AGC circuit consisting of multi-stage AGC amplifiers, and that the intermediate frequency amplifier circuit is controlled by the AGC control voltage when the output voltage of the final stage of the AGC circuit is constant. It detects the input electric field level.

Embodiment of the Invention Next, a preferred embodiment of the present invention will be specifically explained with reference to FIGS. 1 and 2.

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention. In this embodiment, an AGC circuit composed of n-stage AGC amplifiers will be considered.

If the load connected to the output section of the n-th stage is regarded as RL, the output voltage Vo is controlled by the AGC control circuit 2 so that the output voltage 0 becomes constant after being rectified by the rectifying capacitor (3rec). The AGC circuit according to the present invention can obtain sufficient linearity.This will be explained below using mathematical expressions.

The gain g of this AGC circuit can be expressed by the following equation.

■0 ” = V1 block ...... (1) ・　・・・・・・・(2) here ・−・−・・・・・・・・(3) And then It can be expressed as

It becomes. As can be seen from equation (4), g' is the gain obtained by normalizing the gain g by tL (E, +RC) (Rc I 1)n.

Figure 2 shows the dependence of g' (indicated by aB) using l and n as parameters. Here, from equation (5), the AGC control voltage VAG a is proportional to k, so the gain g′ in FIG.
This can be interpreted as indicating the AGC control voltage VAGC dependence of .

As can be seen from FIG. 2, compared to REIll =O(l-0), if, for example, No 2 or l-3 is set, a pseudo-logarithmic characteristic with good linearity can be obtained over a wide range.

Further, the pseudo-logarithmic characteristic region of the gain limit is expanded in proportion to the number of stages n.

As described in detail, the present invention provides an intermediate frequency amplification circuit with a multi-stage A
It consists of an AGC circuit consisting of a GC amplifier, and the input electric field level of the intermediate frequency amplifier circuit is detected using the AGC control voltage when the output voltage of the final stage of the AGC circuit is constant, and only one rectifier is required. . Therefore, only one capacitor is required for the rectifier, and even if a capacitor cannot be built in when lowering the intermediate frequency, the terminal for an external capacitor can be connected to one terminal.
This can be solved by simply adding this book. Further, when the intermediate frequency is lowered, the necessary gain can be obtained even if the current value flowing through each stage of the intermediate frequency amplifier is small, and current consumption can be reduced.

Further, since the electric field detection voltage is not subjected to addition of rectified voltage, etc., it is pseudo-logarithmically compressed with respect to the input electric field level, and does not change almost linearly, but becomes a monotone function. However, since the saturation level for a large input electric field is improved, a sufficient dynamic range of the detected electric field can be obtained.

Furthermore, since the temperature characteristic of the electric field detection voltage also becomes a monotonous linear straight line, temperature compensation can be easily performed.

To summarize the above, according to the present invention, the input electric field level to the intermediate frequency amplifier circuit can be detected by the AGC control voltage,
Furthermore, it is possible to obtain an intermediate frequency amplification circuit with few external components, which is obtained due to the relationship of pseudo-logarithmic characteristics with good linearity, can detect input electric field levels in a wide dynamic range, has excellent temperature characteristics, operates with low current consumption, and has few external components.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a partial block diagram of an embodiment of the present invention. ■IN...Input voltage, Vo...Output voltage, VAG
C・AGC control voltage, VCC-・Power supply voltage, Q ]-1
, ・Q 16 , ・Qnl ＋・・・' 6...
Transistor, Rc, REI, RE2...Resistance, RI,...Equivalent load resistance, Engineering 1...Constant current source, 0
rec... rectifying capacitor, 1... rectifier, 2...
...AGC control voltage generator 2nd CHd 1st figure shows VAGa,! :g=Vo/VIN This is a diagram showing the relationship between g and VIN using l as a parameter. FIG. 3 is a diagram showing an example of a conventional circuit. Ql/~Q50'...Transistor, D1'...Diode, R1'~R43'...Resistor, C31'~C11
'... Capacitor, Vcc... Power supply voltage, S -M
ETEROUT...P electric field detection output terminal FIG. 4 shows the output voltage of S-METEROUT in FIG. 3 with respect to the level V of FIN.

Claims (1)

[Claims] a first differential amplifier in which the emitters of each of the first pair of transistors are connected in common via a resistor; a second differential amplifier whose respective emitters are commonly connected via a resistor; and a third pair of transistors whose emitters each have a resistor connected to the collector of the other transistor of the first pair of transistors. a third differential amplifier commonly connected through the transistor, and a third differential amplifier connected to the collectors of the second and third pair of transistors, respectively, such that the outputs of the second and third differential amplifiers are opposite to each other. AGC consisting of a resistor
It has n stages of amplifiers, and the output of the first stage AGC amplifier is connected to the input of the second stage AGC amplifier.
1) The output of the AGC amplifier at the first stage is connected to the input of the AGC amplifier at the nth stage, and the output from the AGC amplifier at the first stage to the AGC amplifier at the nth stage is connected so that the output of the AGC amplifier at the nth stage is constant. A common to all n-stage AGC amplifiers up to
In the AGC circuit configured to apply a GC control voltage, the AGC control voltage of the AGC circuit has a pseudo-logarithmic characteristic with respect to the input voltage of the first stage AGC amplifier. Frequency amplification circuit.