JPS604321A - Variable gain amplifier - Google Patents

Abstract

PURPOSE:To obtain a broad band variable gain amplifier applicable to a high- quality radio equipment by providing an amplitude changing circuit in the preceding stage of a variable gain amplifying circuit. CONSTITUTION:The gain of a variable gain amplifying circuit V-AMP is controlled by an automatic gain control circuit AGC-CON so that the output level of a terminal 5 is constant approximately even if the input level applied to a terminal 3 is changed by, for example, about 50dB, and the input level applied to the terminal 3 is monitored by an input level detecting circuit DET. Outputs of the automatic gain amplifying circuit AGC-CON and the input level detecting circuit DET are inputted to a driving circuit DRV, and the driving circuit is so operated that the frequency characteristic of a variable gain amplifying circuit V-AMP is compensated by the amplitude characteristic of an amplitude equalizing circuit AE and is made flat as the whole, and this frequency characteristic is applied to the amplitude equalizing circuit AE to improve the frequency characteristic as the whole.

Description

DETAILED DESCRIPTION OF THE INVENTION (81) Technical Field of the Invention The present invention relates to a variable gain (q) amplifier, and particularly to a variable gain amplifier used in radio equipment requiring high quality.

(bl Conventional technology and problems) Both analog wireless systems that send images and other information in analog quantities, and digital wireless systems that digitize information, are used.
are increasing. Along with this, the standards required for radio equipment are becoming more stringent.

For example, for a variable gain intermediate frequency amplifier, the input voltage may vary by 50 to 60 db.
In some cases, it may be required that the frequency characteristic must be flat in the range z or 140±25M1lz.

FIG. 1 is a diagram for explaining the operation of a conventional variable gain amplifier circuit.

In the figure, the intermediate frequency signal applied to terminal 1 is amplified by amplifier IP-1, passes through a circuit in which diodes D1 and D2 are connected in series, and is amplified again by amplifier AMP-2. , taken out from terminal 2. Here, the resistance of the diodes D1 and D2 is determined by the fact that the drive voltage v1 is large (as a large diode current flows, so the resistance of each diode decreases, and conversely, the smaller the drive voltage v1 is, the greater the resistance of the diode becomes. The current i applied from amplifier AMP-1 to amplifier MP-2 is approximately given by v/rdl''rdl, where V is the output voltage of amplifier X::AMP-1.
rd2 are resistance bones of diodes D1 and D2, respectively. As can be seen from this equation, by changing the resistance of the diode, the magnitude of the current applied to MP-2 to the amplifier changes. Therefore, amplifier/IMP-1 and AM
The gain of P-2 itself is determined by the value of the feedback resistor R1 + R2, but by changing the drive voltage v1, the input current to the amplifier AMP-2 can be changed. The gain of the amplifier configured with AMll-2 can be controlled.

FIG. 2 shows the frequency versus output characteristics of the variable gain amplifier circuit introduced in jiL as explained in FIG.

In the figure, ■ indicates a case where the input level to the variable gain amplifier circuit is high, and the gain of the variable gain amplifier circuit is small. (2) is when the input level is standard, and (2) is when the input level is low, and the gain of the variable gain amplifier circuit is large.

As you can see from this figure, the gain of the variable gain amplifier circuit is large (as you can see, the higher frequency response components decrease, while the lower frequency components increase).

This is because the frequency characteristics of the transistors that make up the amplifier appear as they are in order to increase the gain of the variable gain amplifier circuit, or because the influence of stray capacitance becomes noticeable by changing the resistance bones of diodes 'DI and D2. be. Circuits have been devised to compensate for this, but they are not always sufficiently effective, and variable gain amplification circuits using pariorososers have problems such as the circuit scale becoming large and not being able to be miniaturized. .

(C1 Object of the Invention The present invention has been made in view of the problems of the prior art described above, and an object of the present invention is to provide a wideband variable gain amplifier for use in high-quality radio equipment.

(dl Structure of the Invention The object of the invention is to provide a variable gain amplifier circuit for amplifying an intermediate frequency signal, an automatic gain control circuit for controlling the gain of the variable gain amplifier circuit using an output signal of the variable gain amplifier circuit, and a variable gain amplifier circuit for controlling the gain of the variable gain amplifier circuit using an output signal of the variable gain amplifier circuit. In a variable gain amplification section consisting of an input level detection circuit that detects the level of an input signal applied to a gain amplification circuit, the automatic gain 1u control circuit and the output of the input level detection circuit are connected at a stage before the variable gain amplification circuit. This is achieved by providing a variable gain amplifier characterized in that it is provided with an amplitude equalization circuit that is controlled by a drive circuit that combines signals.

tel　Embodiments of the invention FIG. 3 is a block diagram of one embodiment of the present invention.

In the figure, AE is an amplitude equalization circuit, V-AMP is a variable gain amplifier circuit, AGC-CON is an automatic gain 1M control circuit, and I
IET is input level detection circuit, DRV is drive circuit, 3
~7 indicate l, 1.11 children, respectively.

Each of these blocks is connected as follows.

The (1) input terminal of the amplitude equalization circuit AIE is! 111 children 3
and.

The output terminals are respectively connected to the terminal 5 via the variable gain amplifier circuit V-A. Also automatic gain control circuit AGC-CO
The input terminal of N is connected to terminal 5, the output terminal of (1) is connected to input terminal (2) of variable gain amplifier circuit V-AMP, and the output terminal of (2) is connected to terminal 6 of drive circuit DIIV. The input terminal of the circuit DET is the variable gain amplifier circuit V-AMP.
The output terminal (2) of the output terminal is the terminal 7 of the drive circuit DRV, and the output terminals (1) and (2) of the drive circuit DRV are the input terminals (2) and (3) of the amplitude equalization circuit AIE. connected to the respective terminals.

Note that the portion of the present invention is surrounded by a dotted line.

The operation of each block connected in this way is as follows.

The intermediate frequency signal applied to terminal 3 is passed through the amplitude equalization circuit AIE.
And it is outputted to the outside from terminal 5 via variable gain amplifier circuit V-8Ml+. At this time, even if the input ■/her applied to terminal 3 changes by, for example, 50 dh, the automatic gain control circuit AGC is configured to maintain a substantially constant output level at terminal 5.
-CON controls the gain j[) of variable gain amplifier circuit V -AMP, and input level detection circuit DIET controls terminal 3.
monitor the input level applied to the

In this case, the frequency characteristics of the variable gain j11 amplifier circuit V-AMp with respect to the gain are such that the higher the gain, the lower the high frequency components are, as described above, so the way to compensate for this and make the characteristics flat is as shown in the dotted line. In part, automatic gain amplification circuit AG
The outputs of C-CON and the input level detection circuit DIET are input to the drive circuit DRV, and the amplitude characteristics of the amplitude equalization circuit AE are driven to the variable gain amplifier circuit C so that the amplitude characteristics of the amplitude equalization circuit AE are flattened as a whole by compensating for the main frequency characteristics. Create a circuit output and apply it to the amplitude equalization circuit AIE.

FIG. 4 is a more detailed diagram illustrating the operation of the portion surrounded by dotted lines in the block diagram 1-17 shown in FIG.

In the figure, 8E indicates an amplitude equalization circuit, DRE indicates a drive circuit, and 3, 4, and 6.7 indicate terminals, using the same symbols as in FIG. 3.

These parts are connected as follows.

In the amplitude equalization circuit AE, a parallel connection of a bin diode D2 and a varactor diode D3 is inserted between terminals 3 and 4, and the bin diode D2 is connected to the amplifier MP.
-3 and AMP-4, varactor diode-1"D.

are driven by amplifiers AMP'-5 and #AMp-6, respectively.

Then, both MP-3 and AMI'-5 are connected to terminal 6 to the amplifier.
and 7 to the automatic gain control voltage 8GC-CON and the output signal of the input level detection circuit DET.

The function of this circuit is to compensate the frequency characteristics of the variable gain amplifier circuit V-A with the frequency characteristics of the amplitude equalization circuit An, as described above, and the drive unit DRV that drives this amplitude equalization circuit AE. The operating point of is set using the following steps.

1. Measure the frequency characteristics of the variable gain amplifier circuit V-AMP to determine the amount to be compensated (see Figure 2).

2.? In order to realize the frequency characteristics to be compensated for, the bin diode D2 is replaced with a resistor, and the varactor diode D3 is replaced by a capacitor, and the frequency characteristics of these parallel circuits are set so that they approximately match the frequency characteristics to be compensated for in the first term. Figure 5 (see al) to determine the value of.

3. Vin diode D2 and varactor diode DP
The drive voltage and drive current are determined from the characteristic curve of each element so that the resistance and capacitance become the values determined in the second term (see FIG. 5 (bl)).

4. Combine the curves of the input voltage detection voltage and the automatic gain control voltage (see tel in FIG. 5), not shown in FIG.

5. Set the values of the variable resistors Rc1 to Rv-(i) shown in FIG. 4 to match the control curve in Section 4.
Finally, while directly observing the frequency characteristics of the variable gain amplifier circuit V-AMP,
the value of? ! i, MI! II Adjust.

Through the above adjustments, the variable gain amplifier circuits VA, MI
+ profit i! Flat characteristics can be obtained over the entire necessary frequency band regardless of l.

FIG. 6 shows another embodiment of the present invention.
2 and varactor diode-1-D3 connection in Figure 6 fat
In the case of series connection, Figure 1 (t) is connected in series, Figure 1 (t) is connected in series, Figure 6 (al
The resistor I? is also connected in series, but in order to lower the 0 value of the varactor diode r13 and achieve a wider band, the resistor I? 5 are connected in parallel to the varactor diodes 1 and D3.

Also in this case, by arranging variable resistance elements and variable capacitance elements in series and in parallel, a circuit having arbitrary frequency characteristics can be constructed.

Figure 7 shows another example of the present invention! In example i, drive circuit DVI
? The configuration is different from that in FIG.

In the case of No. 7 (a), the variable resistor is connected to the terminal 7 and the amplifier AMP.
-7 and AMP-9, amplifiers AMP-7 and 8 are inserted between MP-8, and amplifiers AMP-9 and AMP-10, respectively.

Figure 7 (In the case of bl, the variable resistor is connected to terminal 6 and the amplifier M
Between P-11 and eight MP-13, MP- to amplifier
They are inserted between the output side of AMP-11 and the input terminal (1), and between the output side of AMP-13 and the input terminal (1), respectively.

However, it is functionally the same as in FIG.

(fl As described in detail, according to the present invention, an amplitude equalization circuit is constructed using a bin diode and a varactor diode,
The frequency characteristics of the variable gain amplifier circuit can be compensated by driving the amplitude equalization circuit with a drive voltage obtained by suitably combining the output voltages of the automatic gain control circuit and the input level detection circuit. Therefore, by adding the circuit of the present invention to the conventional variable gain amplifier circuit, it can be used in high quality radio equipment.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the operation of a conventional variable gain amplifier circuit, Fig. 2 is a diagram showing the frequency vs. output characteristic of the circuit shown in Fig. 1, and Fig. 3 is a diagram for explaining an embodiment of the present invention. Block diagram shown,
FIG. 4 is a more specific circuit diagram of one embodiment of the present invention, and FIG.
Figures (a), (bl, (C1 is a diagram for explaining the operating point setting of the drive circuit included in one embodiment of the present invention, the sixth figure is
Figures Another Embodiment of the Invention FIG. 7 shows another embodiment of the invention. In the figure, 8 [amplitude equalization circuit] - MP is a variable gain amplifier circuit AGC-CON is an automatic gain control circuit, DIIV
is the drive circuit, T is the input voltage detection circuit, D is the bin diode, D= is the varactor diode, to MP-3
~8 MP-14 is an amplifier, I? , ~R5 is the resistance, 1 to 7
indicate the respective terminals.煕I block 1 to 4 (guest 3 后#4-to close, 1 adult power rehe+shi→〆

Claims (1)

[Claims] A variable gain amplifier circuit that amplifies an intermediate frequency signal, an automatic gain control circuit that controls the gain of the variable gain amplifier circuit using an output signal of the variable gain amplifier circuit, and detects the level of an input signal applied to the variable gain amplifier circuit. In a variable gain amplification section consisting of an input level detection circuit, the automatic gain control circuit and the input port 1 are provided before the variable gain amplification circuit.
1. A variable gain amplifier characterized by being provided with an amplitude equalization circuit controlled by a drive circuit that synthesizes the output signals of the detection circuit.