JPS6240851A - Multivalue qam demodulating circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration in an error rate by shifting one phase of a carrier wave by a control signal obtained from a reproducing data and an error signal, and making it coincide with a phase of a carrier wave of a transmission side. CONSTITUTION:A phase of a carrier wave of a reception side is made to coincide with a phase of a carrier wave of a transmission side by controlling a phase-shifting quantity of a variable phase shifter 12 by an output corresponding to one calculation result of I2+epsilon1 or I1+epsilon2 from reproducing data signals I1, I2 which have been applied to a controlling circuit 11 from data reproducing discriminators 6, 7, and error signals epsilon1, epsilon2. Even if a phase of a carrier wave of a transmission side is shifted by 90 deg. or more, the follow-up can be executed with a high accuracy in the reception side.

Description

[Detailed Description of the Invention] [Summary] In a multi-value (JAM demodulation circuit), one phase of substantially orthogonal carrier waves applied to a quadrature detector is controlled using an error signal from a data reproduction discriminator and reproduction data. The phase was shifted by a variable phase shifter controlled by a signal to match the nearly orthogonal carrier wave applied to the transmitting side quadrature modulator.

This substantially eliminates deterioration in the error rate of reproduced data extracted on the receiving side.

[Industrial application field]

The present invention relates to an improvement of a multilevel OAH demodulation circuit used in a digital radio device.

It is difficult to match the phase of the carrier wave supplied to the quadrature detector for quadrature detection of the multilevel 01M wave with the phase of the carrier wave applied to the quadrature modulator on the transmitting side due to the accuracy of the measuring instrument.

On the other hand, in order to improve transmission efficiency, 640AM, 256
As 0AM and multilevel modulation methods progress, orthogonal interference increases due to the above-mentioned phase mismatch, and the error rate of demodulated data deteriorates.
M demodulation circuit is required.

[Prior Art] FIG. 3 shows a block 1 diagram of a conventional example, and 4th [xl] shows an operation explanatory diagram of FIG. 3.

In FIG. 3, -C1, for example, a multivalued gate wave converted to an intermediate frequency band is divided by a hybrid circuit 1 and applied to a quadrature detector 2.3.

Here, a voltage controlled oscillator (hereinafter abbreviated as VCO) 1
Since the output of 0 is converted into an orthogonal carrier wave by the 90 degree vibrator 1' circuit 9, multi(l!1Ifl A
The M wave is detected and the base Han l (No. 8 is extracted, low frequency) fffffl is used to limit the band or remove the high frequency component using an under-filter. taken out.

Here, the error signal ε is a signal that indicates whether it is higher or lower than the original level by 1.0.

The front sound is sent from the terminal OUT and 0UT-2, but
The first bit 11 of lji 1f and I! and the latter is applied to the drive circuit 8 with +JI+elane, ([,■ε,)-(1,
■ ε2) calculation (here, ■ indicates exclusive OR) is performed, but since the result shows the phase error of the single most transmitted wave on the transmitting side and the receiving side, the phase error is calculated from this circuit 8. S・Niri・t
A voltage of It, .

The circuit that executes the calculation is 1. and B2 and 12. and ε,
Then, the DC component is obtained by integrating the exclusive OR of and, and the difference is 11y using a differential amplifier.

For example, as shown on the left side of FIG.

■3') are orthogonal to each other 7, and when the sending (the orthogonal axes on the a side and the receiving side are θ+), the drive circuit 8 Control is performed in the direction of the arrow so that B and [3'' coincide with each other, and the orthogonal axes of the carrier waves on the transmitting and receiving sides are completely defeated.

However, as shown in Figure 4 (bl), the carrier waves on the transmitting side are orthogonal, but the carrier waves on the receiving side are not orthogonal. is 0
Even if B and B1 match, the angle between A and Ao will be θ1 - θ2, and an error of 1: will remain (center diagram in Figure 4).

Then, 8゛ approaches Δ, B and B1 move away, and 4゛■ε
The difference is 0 when the values of I) and (1, G)B2) are equal.
Therefore, control stops.

That is, as shown on the left side of FIG. 4, fhl, both of them are finally stabilized and stopped at half the error percentage (.theta.1-.theta.2.).

[Problem that the invention seeks to solve]

As explained in detail above, there is a problem that the error rate deteriorates because a phase error remains between the carrier wave on the receiving side and the carrier wave on the transmitting side.

[Means for solving problems]

The above problem is solved by the variable phase shifter 12 that shifts the phase of the carrier wave, and the variable phase shifter 12 that shifts the phase of the carrier wave so that the phase of the carrier wave matches the phase of the transmitting side carrier wave using reproduced data and an error signal. The multi-level QAM of the present invention is provided with a control circuit 11 for controlling
This problem is solved by a demodulation circuit.

[Effect]

The present invention provides data rez1 identification i! With the control signal obtained by the control circuit 11 from the reproduced data and error signal from IT6.7, the phase of the carrier wave with a phase difference of approximately 90 degrees is added to the quadrature detector No. 2.3. The phase is shifted by a phase shifter 12 to match the phase of the carrier wave on the transmitting side. Therefore, the deterioration of the error rate is almost eliminated.

〔Example〕

The contents of the present invention will be specifically explained below with reference to illustrated embodiments. Note that the same reference numerals refer to the same objects throughout the plan.

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
The operation explanatory diagram of the figure is shown. The dotted line portion in FIG. 1 indicates the portion added according to the present invention.

In FIG. 1, I, . B1. B2 to 1. Which one of ■ε1 or I, ■ε (for example, l
, (denoted as Dε2) controls the phase shift amount of the variable phase shifter 12 to match the phase of the carrier wave on the receiving side with the phase η of the carrier wave on the transmitting side. It is done as follows. That is, when the phase state of the carrier waves on the transmitting and receiving sides is as shown in the diagram on the left side of FIG. 2 (same as the diagram on the right side of FIG. For example, if we make Bo match B and break the balance, we get the same <A, != as above.
Since there is a phase error between A', it moves in the direction of the arrow and A'
approaches 8, B1 and 13 separate and stop at the same phase error (center of Figure 2). Therefore, control circuit 1
If the balance is broken again by control from 2, the error signal approaches 0, and as shown on the right side of Figure 2, control stops when A and A' and B and Bo match, and the receiving side The phase of the carrier wave matches the phase of the transmitting side.

The control circuit 11 includes an exclusive OR circuit III that performs a calculation of (1, ε2), an integration circuit 112 that extracts a DC part from the output of this circuit, and a buffer amplifier 113, and a variable phase shifter 1.
2 may be a phase shifter that shifts the phase of a carrier wave of, for example, 70 MIIz or 140 M1lz by several degrees, so it can be realized with a simple configuration.

〔Effect of the invention〕

As explained in detail below, even if the phase of the carrier wave applied to the quadrature modulator on the transmitting side is shifted by more than 90 degrees, it can be followed accurately on the receiving side, so there is almost no deterioration in the error rate ( There is an effect that.

Figure 3 is a block diagram of the conventional example. FIG. 4 shows an explanatory diagram of the operation of FIG. 3.

In the figure, 11 is a control circuit; 12 indicates a variable phase shifter.

Lu box

Claims (1)

[Claims] Multi-level QA using a carrier wave from a voltage controlled oscillator (10)
When the data reproduction discriminator (6, 7) extracts reproduced data and error signals from the baseband signal obtained by quadrature detection of the M wave, a variable phase shifter ( 12), and a control circuit (11) that controls the variable phase shifter so that the phase of the carrier wave matches the phase of the transmitting carrier wave using the reproduced data and the error signal. Multilevel QAM
Demodulation circuit.