JPS608653B2 - Distortion cancellation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for removing distortion of an amplifier device in, for example, a high frequency broadband repeater.

When creating a wideband amplification device for high frequencies, distortion of the amplifier becomes a problem.

Second-order distortion can be avoided, for example, by push-pull amplification, but odd-order distortion cannot be removed.

For example, if cross-modulation occurs due to third-order distortion of the amplifier for inputs of two frequencies f, , f2, ±f2, public frequency f2,
Since third-order harmonic components such as . Generally, when the frequency is not high, a negative feedback circuit is used to obtain amplifier performance with low distortion.
As the frequency increases, the phase rotation becomes larger, and depending on the frequency, it may oscillate, making it unusable.

In such a high frequency region, the feedforward (fee
dforward) amplifiers are used, but they have the drawbacks of complex construction and inconvenient delay adjustment. As a simple circuit, there is a circuit that uses the nonlinearity of a diode to cancel the distortion of the amplification, but the cancellation is incomplete and has the disadvantage that second-order distortion occurs. SUMMARY OF THE INVENTION It is an object of the present invention to provide a circuit that eliminates the above-mentioned drawbacks and cancels particularly important third-order distortion with a relatively simple configuration.
an amplifier, a voltage transformer to which the high frequency input signal is input together with the first amplifier and boosts the signal at a predetermined ratio, and an output obtained by combining the outputs of the first amplifier and the voltage transformer. This can be realized by a distortion canceling circuit having a second amplifier having the same characteristics as the first amplifier to which a signal is input.

The present invention will be explained in detail below. The figure shows one embodiment of the distortion canceling circuit according to the present invention, in which the input signal V, is amplified by the amplifier 101 and outputs the output voltage V2, and the input signal V,
is also applied to the voltage transformer 20, and the voltage is multiplied by P to output a voltage ball V, and the output voltages V2 and pV are combined and input as a voltage V4 to the amplifier 301 to obtain a voltage V5.

Here, it is assumed that the amplifiers 10 and 30 have the same characteristics, high input impedance and low output impedance, and second-order distortion can be ignored. It is also assumed that the voltage transformer 20 has a sufficiently high input impedance, a sufficiently low output impedance, and is a unidirectional distortion-free circuit. The output voltage V2 of the amplifier 10 can be expressed as follows.

V2=aVI+CV-tei=VI<a+CV-tei) -
...--(1) The output of the voltage transformer 20 is the input voltage v. is p
It is multiplied by pv.

The voltage obtained by combining this pv and the output voltage v2 becomes the input voltage v4 of the amplifier 30, and is expressed as V4=V[(a+p)0CVtei]...[21].

Therefore, the final stage output voltage v5 is expressed by the following equation. V5=
V4 (a+CV reed) =v, [(a+p)a+{a+(a+p)3}cv33(a+p)2C2Vko+3(a+p)C3VWatariC4
〆〆〆〆〆〆〆〆〆〆〆〆From equation {3), the first-order, that is, the fundamental wave component vo, is v.

,=(a0p)av, ...[The 413rd-order distorted wave component vo3 is v.

3 = {a ten (a ten p) 3 } c be ... [51
From the formula ■, the condition for third-order distortion wave cancellation is as follows: p=-a
-3 zo a...(61 formula (6'
Substituting into the formula (4}, we get v〇,=-3ノa.av,
...(7) is obtained, but the meaning of equation {7} is that in the distortion canceling circuit shown in FIG. It shows that the gain is a.

Therefore, if the gain of the front stage is represented digitally and the multiplier P of the voltage transformer 20 is determined to be one-third of the gain of the rear stage, the third-order distortion is canceled out. As is clear from the above description, according to the distortion canceling circuit according to the present invention, third-order distortion can be canceled by appropriately selecting the multiplication factor P of the voltage transformer. By using, for example, a push-pull amplifier as 30, it is possible to realize an amplification device free of second-order and third-order distortion.

[Brief explanation of drawings]

The figure is a block diagram for explaining the distortion canceling circuit of the present invention. In the figure, an amplifier 10, 30' and a voltage transformer 201 are shown.

Claims (1)

[Claims] 1 a first amplifier that amplifies a high frequency input signal;
The high-frequency input signal is inputted together with the amplifier, and the voltage transformer boosts the voltage at a predetermined ratio, and the output signal obtained by combining the outputs of the first amplifier and the voltage transformer is inputted. A distortion cancellation circuit comprising a second amplifier having similar characteristics to the first amplifier.