JPS5850444B2 - auto-balanced amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a balanced amplifier circuit for obtaining a difference output between two human input signals, and particularly to a balanced amplifier circuit for obtaining a differential output of two human input signals, and particularly for a frequency conversion circuit when used for synthesizing intermediate frequency outputs of a balanced line frequency conversion circuit. This invention relates to an automatically balanced amplifier circuit that maintains good balance as a whole.

Balanced line frequency conversion circuits are widely used as frequency conversion circuits with a low noise figure.

Particularly in cases where the local oscillator itself generates a large amount of noise, such as an in-bat oscillator, the noise reduction effect of using a balanced type is significant.

However, such low noise can be obtained by combining two frequency converters and both outputs... an hybrid circuit,
Alternatively, the differential amplifier may be perfectly balanced, and if the balance is lost, the characteristics will deteriorate rapidly.

Generally, the conversion loss of a frequency converter is influenced by local power, but it is extremely difficult to sufficiently equalize the effects of local power in two frequency converters.

In other words, unless the local power is sufficiently stable, sufficient low-noise characteristics cannot be obtained.

An object of the present invention is to provide a balanced amplifier circuit that can be used in a balanced line frequency conversion circuit to automatically maintain balance and achieve low noise characteristics.

The present invention will be explained in detail below using the drawings.

FIG. 1 is a block diagram showing an example of a conventional balanced line frequency conversion circuit, in which an input signal applied from a terminal 1 is divided into two equal parts by a hybrid 2 and applied to frequency converters 3 and 4.

At the same time, the local oscillation signal from the local oscillation signal source 5 is also divided into two equal parts by the hybrid 2 and applied to the frequency converters 3 and 4.

However, due to the phase characteristics of the hybrid, frequency converters 3 and 4
The phases of the local oscillator signals applied to are opposite to each other.

Therefore, the intermediate frequency signals of the difference frequency between the input signal and the local signal obtained from the frequency changers 3 and 4 have opposite phases.

These intermediate frequency signals are synthesized by a hybrid transformer 6 through terminals 7 and 8, and appear at a terminal 9, where they are output to an intermediate frequency amplifier 1.
After being amplified by 0, it is obtained at the output terminal 11.

At this time, the noise contained in the local signal source appears at the terminals 7 and 8 in the same phase, so it is canceled out by the action of the hybrid transformer 60 and does not appear at the terminal 9.

This is the operating principle by which conventional balanced line frequency conversion circuits exhibit low noise characteristics.

However, in order to completely cancel out the noise, the frequency converter 3
The conversion losses of .degree. 4 must be exactly the same, and the balance of the hybrid transformer 6 must be good.

However, as mentioned above, it is generally not always easy to maintain this balance well.

FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention.
Reference numerals 12 and 13 are signal input terminals, which correspond to terminals 7 and 8 in FIG. 1 when this automatic balanced amplifier circuit is used as a part of a balanced line frequency conversion circuit.

The signals applied from the terminals 12 and 13 are amplified by gain-controllable amplifiers 14 and 15, and the sum of the outputs of the stage width amplifiers is taken by an adder circuit 16, and the difference is taken by a subtracter circuit 17.

The difference signal is output from the terminal 18 as an output signal of the balanced amplifier circuit, and at the same time is multiplied by the sum signal in the multiplier circuit 19.

This product signal is amplified by an amplifier 20 and fed back through a low pass filter as a gain control signal for the amplifier 14.150.

In this circuit, input terminals 12 and 13 each have s+
Suppose that signals n and α(-s+n) are added.

Here, S is a desired intermediate frequency signal, n is noise, and α is a coefficient indicating the degree of balance between the two frequency converters, and is a quantity that is 1 when the two frequency converters are perfectly balanced.

The reason why this coefficient α is common to S and n is that the conversion loss of the frequency converter acts equally on both signals and noise.

Assuming that the gains of the amplifiers 1415 are A1 and A2, the output of the adder circuit 16 is A1 (s+n) + A2α (-8+n
), and the output of the subtraction circuit 17 is A1(s+n)-A2
α(-8+n).

Therefore, the product of both these signals is (A1-cc2A2) (s
2+n2) + (AF+α2Aj) 4 sn
becomes.

When this signal is amplified and only the low frequency component is extracted, the second term is a noise component with an average value of O and is almost blocked by the low pass filter.

On the other hand, since the term (s2+n2) in the first option means the sum of the power of the signal and the noise, a voltage K (AZAζα2) is obtained in which a constant k proportional to this average power is applied as a coefficient.

If this voltage is positive, the gain of the amplifier 15 is increased and the gain of the amplifier 14 is decreased, and if this voltage is negative, the gain of the amplifier 14 is increased and the gain of the amplifier 15 is decreased. AI' alone: α2 = 0.

In other words, A1 hole 2α(-A).

When this relationship holds, the output of the subtraction circuit 17 becomes 2As and does not include noise n.

In other words, the unbalance of the frequency converter is corrected, and a frequency conversion circuit that is balanced as a whole can be realized.

In the above description of the embodiment, a case has been shown in which the gains of the amplifiers 14 and 15 are controlled in opposite directions, but this is not necessarily necessary, and the purpose of the present invention can be achieved by controlling the gain of either one of the amplifiers. can be reached.

As described above, according to the present invention, it is possible to obtain an automatically balanced amplifier circuit that can be used in a balanced line frequency conversion circuit to automatically correct the balance and keep the noise figure low at all times. This is extremely effective for use in communication equipment that uses a large oscillator as a local signal source.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional balanced line frequency conversion circuit, and FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 12 and 13 are signal input terminals; Output terminal, 14.15 is an amplifier capable of gain control, 16
17 is a subtraction circuit, 19 is a multiplication circuit, 20 is an amplifier, and 21 is a low-pass filter.

Claims (1)

[Claims] In a balanced amplifier circuit that includes an independent amplifier for each of the 12 human power signals and extracts the difference between the outputs of both amplifiers as a balanced output, there is a difference circuit that extracts the difference between the outputs of both amplifiers, and a sum circuit that extracts the sum of the outputs of both amplifiers. , a multiplier circuit that extracts the product of the difference circuit output and the sum circuit output, and a circuit that extracts the low frequency signal component of the multiplier circuit output signal, at least one of the amplifiers is a variable gain amplifier, and the gain of the amplifier is set to the An automatic balancing amplifier circuit characterized in that it is configured to be controlled by a circuit output that extracts low frequency signal components.