JP3308811B2 - Quadrature modulator with gain control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention suppresses a carrier leak which causes deterioration of an error rate of a received signal on a receiving side when performing quadrature modulation such as a QPSK modulation method in a mobile radio communication device such as a portable telephone. The present invention relates to a quadrature modulator with a gain control circuit.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an example of a conventional quadrature modulator with a gain control circuit. In the figure, reference numeral 1 denotes a first mixer, 2 denotes a second mixer, and 3 denotes a first adder. 4 is 90 °
5 is a gain control circuit, 6 is an output amplifier, 7 is a carrier input terminal, 8 is a baseband I signal input terminal, 9 is a baseband Q signal input terminal, 10 is a quadrature modulation circuit, and 18 is a quadrature modulator. Output terminals, each of which is connected as shown. First, the carrier wave input terminal 7
2 signals are orthogonal with 90 ° phase shifter 4 carrier input from COS (ω _c t), the process branches to SIN (ω _c t). One of the split carrier waves is input to the first mixer 1, and the first
Is multiplied by the baseband I signal input to the mixer 1.
The other branched carrier wave is input to the second mixer 2 and similarly multiplied by the baseband Q signal input to the second mixer 2. Next, a first mixer 1 and a second mixer 2
Are added by the first adder 3 to generate a modulated wave signal. This modulated wave signal is input to the gain control circuit 5,
After gain control, the signal is amplified by the output amplifier 6 and output from the quadrature modulator output terminal 18.

As means for suppressing the carrier leak, the control voltage of the gain control circuit 5 is maintained at a certain value, and the output level of the modulated wave signal at the quadrature modulator output terminal 18 is fixed. The DC bias values of the quadrature baseband signals I and Q to be input to 10 are adjusted to suppress carrier leak.

The causes of such carrier leakage in the quadrature modulator include DC offsets of the quadrature baseband signals I and Q input to the quadrature modulation circuit, and the relative occurrence between elements such as resistors constituting the quadrature modulation circuit. For example, when the quadrature modulator is integrated into a small package such as an SSOP, the local signal input to the modulator IC may be interfered by lack of isolation on a chip or between terminals and bonding wires. Is I
Interfering with the high impedance circuit part on the C chip,
It is conceivable that the carrier may be output as a carrier leak by interfering with an output terminal of the quadrature modulator or a bonding wire. The amount of leakage and the phase are adjusted, and this is added to the carrier leaked due to mutual interference due to lack of isolation, for which the absolute amount is fixed, and the carrier leak appearing at the output terminal of the quadrature modulator is apparently canceled. .

[0005]

However, in the quadrature modulator with a gain control circuit, when gain control is performed by the gain control circuit, the output level of the modulated wave signal output from the modulation circuit is controlled at the same time as the original level. Since the carrier leak amount due to the DC offset is also controlled, there is a problem that the carrier leak apparently canceled at the output terminal of the quadrature modulator by adding the carrier offset breaks its balance, and the carrier leak increases.

An object of the present invention is to provide a quadrature modulator with a gain control circuit capable of suppressing an increase in carrier leak even when gain control is performed. I do.

[0007]

A quadrature modulator with a gain control circuit according to the present invention directly modulates quadrature baseband signals I and Q.
Multiply each carrier with the cross-phase relationship and perform amplitude modulation.
A quadrature modulation circuit for adding a modulated signal and outputting a modulated wave signal ;
A gain control circuit Gosuru gain system a modulated wave signal from the quadrature modulation circuit, and cancellation carrier signal control circuit for outputting a signal having an arbitrary phase and amplitude by multiplying the carrier wave and any DC value, gain control And an adder for adding the output signal of the canceling carrier signal control circuit to the modulated carrier signal.
By adjusting the C value, it appears at the output of the quadrature modulator.
The carrier leakage is controlled .

According to this invention, even when the gain control of the quadrature modulator is performed by adding the modulated wave signal output from the gain control circuit and the cancel carrier signal output from the cancel carrier signal control circuit. In addition, it is possible to suppress an increase in carrier leak of the output of the quadrature modulator.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same reference numerals are used for the same parts as those of the conventional one. FIG. 1 is a block diagram showing a configuration of a quadrature modulator with a gain control circuit according to an embodiment of the present invention. In the figure, 1 is a first mixer, 2 is a second mixer, and 3 is a first adder. , 4 is a 90 ° phase shifter, 5 is a gain control circuit, 6 is an output amplifier, 7 is a carrier wave input terminal, 8 is a baseband I signal input terminal, 9 is a baseband Q signal input terminal, and 10 is a quadrature modulation circuit. , 18 are output terminals of the quadrature modulator, and the configuration up to this point is the same as that of the conventional one. The present invention is obtained by adding a cancel carrier signal control circuit to this conventional configuration.
11 is a third mixer, 12 is a fourth mixer, 13 is a second adder, 14 is a third adder, 15 is a first variable resistor, 16 is a second variable resistor, 17 is A cancel carrier signal control circuit is shown and connected as shown. The overall principle configuration is as shown in the block diagram of FIG.

Next, the operation will be described. 2 signal COS orthogonal carrier input from the carrier input terminal 7 by the 90 ° phase shifter 4 (ω _c t), the process branches to SIN (ω _c t). One of the split carrier waves is input to the first mixer 1 and similarly multiplied by the baseband I signal input to the first mixer. The other branched carrier wave is input to the second mixer 2 and is similarly multiplied by the baseband Q signal input to the second mixer. The output signals of the first mixer and the second mixer are added by a first adder 3 to generate a modulated wave signal. This modulated wave signal is input to the gain control circuit 5 and, after gain control, is input to the third adder 14. Further, one carrier wave branched into two signals orthogonal to each other by the 90 ° phase shifter 4 is input to the third mixer 11, and an arbitrary carrier generated by the first variable resistor 15 similarly input to the third mixer 11. Is multiplied by the DC value X1. The other split carrier is input to the fourth mixer 12, and similarly the fourth
Is multiplied by an arbitrary DC value X2 generated by the second variable resistor 16 input to the mixer 12 of FIG. Third mixer 11 and fourth mixer
When the output signal of the mixer 12 is added by the second adder 13, the added output becomes as shown in (Equation 1).

[0011]

[Number 1] ^{SQR (X1 2 + X2 2)} * COS (ω c t + tan ~
¹ (X2 / X1)), and the amplitude and phase of the carrier signal can be arbitrarily set by changing the DC values X1 and X2. The output signal of the second adder 13 and the output signal of the gain control circuit 5 are input to a third adder 14 and the added signal is output. This output signal is input to the output amplifier 6. Then, the signal is output from the quadrature modulator output terminal 18.

Here, it is assumed that the output of the gain control circuit 5 input to the third adder 14 without inputting the baseband I signal and Q signal input to the first and second mixers 1 and 2 is turned off. The carrier leak appearing at the output of the output amplifier 6 is considered to be only a component generated by the input carrier wave electromagnetically interfering with each other due to insufficient isolation on the chip or between terminals or between bonding wires. Therefore, since the amplitude and phase of the carrier wave output from the second adder 13 can be arbitrarily set, the cancel signal input to the third adder 14 is changed so that the carrier leak output from the output amplifier 6 is minimized. By adjusting the DC values X1 and X2 input to the third and fourth mixers 11 and 12 by the first and second variable resistors 15 and 16, the cancel signal is added and generated by the second adder 13. This cancels the carrier leak component generated by the electromagnetic mutual interference at the output section of the output amplifier 6, and the carrier leak does not appear apparently.

Since the absolute amount of the component of the carrier leak generated by the mutual interference is determined by the IC in which the quadrature modulator is sealed unless the input level of the carrier is changed, the third and fourth mixers 11 are once used. , 12 are adjusted by the above-described method, carrier leakage due to electromagnetic interference does not appear at the output terminal 18 of the quadrature modulator. After the adjustment is completed, the baseband I signal and the Q signal are input to the first and second mixers 1 and 2, and the baseband I and Q signals are minimized by a normal method so that the carrier leak of the quadrature modulator output is minimized. By adjusting the DC value of the Q signal, even if the output level is changed by controlling the gain control circuit 5, the relative amount between the modulated wave signal and the carrier leak does not change, and the modulated wave signal output from the modulating circuit is not changed. The conventional problem that the amount of carrier leakage is controlled at the same time as controlling the output level is solved.

As described above, according to the present embodiment, even if the output level of the modulated wave signal is changed by controlling the gain of the gain control circuit, it is possible to prevent an increase in carrier leakage accompanying the change.

[0015]

As described above, according to the present invention, the carrier leak due to the electromagnetic interference is added to the cancel signal at the subsequent stage of the gain control circuit to cancel the carrier leak at the output of the quadrature modulation circuit. Even if the output level of the modulated wave signal is changed by controlling the gain of the gain control circuit,
Since the relative amount between the modulated wave signal and the carrier leak does not change, an advantageous effect that an increase in carrier leak due to the gain control of the gain control circuit can be prevented can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a quadrature modulator with a gain control circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a basic configuration of a quadrature modulator with a gain control circuit according to an embodiment of the present invention.

FIG. 3 is a block diagram showing an example of a configuration of a conventional quadrature modulator with a gain control circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st mixer, 2 ... 2nd mixer, 3 ... 1st adder, 4 ... 90 degree phase shifter, 5 ... Gain control circuit, 6
... output amplifier, 7 ... carrier wave input terminal, 8 ... baseband I signal input terminal, 9 ... baseband Q signal input terminal, 10 ... quadrature modulation circuit, 11 ... third mixer, 12 ...
Fourth mixer, 13 second adder, 14 third adder, 15 first variable resistor, 16 second variable resistor, 17 cancel carrier signal control circuit, 18 quadrature Modulator output terminal.

Claims (1)

(57) [Claims] 1. A quadrature modulation circuit quadrature baseband signals by multiplying each carrier wave with the I and Q in quadrature phase relationship by adding the amplitude modulated signal and outputs a modulated wave signal, this
A gain control circuit for controlling the gain of the modulated wave signal from the quadrature modulation circuit; a cancel carrier signal control circuit for multiplying the carrier by an arbitrary DC value to output a signal having an arbitrary phase and amplitude; An adder for adding a wave signal and an output signal of the cancel carrier signal control circuit, wherein the DC input to the cancel carrier signal control circuit is provided.
A quadrature modulator with a gain control circuit, which controls a carrier leak appearing at an output section of the quadrature modulator by adjusting a value.