JP2000174833A - Carrier suppression feedback circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance detection accuracy of magnitude of a carrier leakage by controlling the phase and the amplitude of a 2nd carrier output, so as to maximize the output of a difference between detection levels of output levels of an orthogonal modulation means detected respectively by 1st and 2nd detection means. SOLUTION: An adder 7 combines a carrier cancel signal received from a level adjustment device 4 and an output of an orthogonal modulator 1 and transmits a combined output. A level detector 5 detects the output level of the orthogonal modulator 1, and a level detector 5 detects a level of the synthesized output. A subtractor 8 calculates the difference between the detected outputs by the level detectors 5, 6. The subtractor 8 gives an output including a modulation signal component that is zero and the difference between carrier leakage signals required for control to a gain setting section 9 and a phase setting section 10. The gain setting section 9 and the phase setting section 10 adjust a 180-degree phase shifter 3 and the level adjustment device 4 so as to maximize the output level of the subtractor 8. Thus, the adder 7 can transmit the modulation signal where the carrier leakage components are cancelled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to suppression of carrier leak of a quadrature modulation circuit used in a modulation device in a system in which a modulation signal fluctuates due to disturbance such as temperature fluctuation and transmission power control or amplitude modulation in digital communication. It relates to a feedback circuit.

[0002]

2. Description of the Related Art FIG. 11 is a block diagram of a main part of a conventional example.

In the figure, 1 is a quadrature modulator, 2 is a local oscillator, 3 is a 180-degree phase shifter, 4 is a level adjuster, 7
Denotes an adder, 100 denotes a 90-degree phase shifter, 101 and 102 denote multipliers, and 103 denotes an adder.

In the figure, A is a DC offset difference between I and Q, B is an I / Q amplitude ratio, C is a variable attenuator attenuation ratio, and φ is I−
The phase error between Q and ψ indicate the phase shifter error, respectively.

The operation of FIG. 11 will be described below. This figure shows a circuit for suppressing carrier leakage caused by a quadrature modulator by adding a wave having the same phase and the same amplitude as that of the carrier to the output of the quadrature modulator. It is.

Now, A + B cos (ωt +
phi) is, cos input terminal Q (ωt + π / 2) is, in 90-degree phase shifter 100 and 180 degree phase shifter 3, the carrier cos omega _c t from the local oscillator 2 and it it added.

[0007] The output x of the quadrature modulator 1 at this time (t) is _{x (t) = Acosω c t-} (1/2) [B 2 -2Bcosφ + 1] 1/2 × sin {(ω + ω c) t + θ 1} ^{- (1/2) [B 2 +} 2B cosφ + 1] 1/2 × sin {(ω- ω c) t + θ 2} ·· (1) = A cos ω c t + Z (t) ·· (1) ' , where , Θ ₁ = -tan ^-1 ｛(B cosφ-1) / (B sinφ)｝ θ ₂ = -tan ^-1 ｛(B cosφ + 1) / (B sin φ)｝ Z (t): modulated wave and image leak As shown in (1) ′, carrier leakage occurs in proportion to the DC offset difference A between the IQ signals.

This carrier leak can be eliminated by setting A = 0. However, although it is possible to reduce it in an actual circuit, it is extremely difficult to eliminate it.

[0009] Therefore, a part of the carrier supplied to the quadrature modulator is demultiplexed, controlled so as to have the same phase and the same amplitude as the carrier leak, and coupled to the output of the quadrature modulator to further reduce the carrier leak. Reduce.

[0010] The output obtained in this way, y (t) = A cos (ω c t) + Z (t) + Ccos (ω c t + π + ψ) = Csinψ × sin (ω c t) + (A- Ccosψ) _{× cos (ω c t) +} Z (t) = [A 2 + C 2 - 2A Ccosψ] 1/2 × sin (ω c t + θ) + Z (t) ··· (2) In addition, theta = -tan ^{- 1} ｛(A- Ccosψ) / (C sinψ)｝.

Here, assuming that the ratio of the carrier leak and the opposite-phase carrier to be synthesized is D, that is, D = C / A, y (t) = A [D ² -2Dcosψ + 1] ^1/2 × sin (ω _c t + θ) + Z (t) (3)

[0012]

In the prior art, C (
Variable attenuator attenuation ratio) and ψ (phase shifter error) are determined by the output amplitude x (t) of the quadrature modulator 1 or the output amplitude y (t) obtained by further reducing the carrier leak from the amplitude x (t). Is monitored and the output amplitude is minimized (see FIG. 11).

Here, when monitoring the output amplitude x (t), x
Since (t) does not change with C and ψ, it is necessary to assume that the amplitude of x (t) is constant.

[0014] On the other hand, to monitor the output amplitude y (t), for detecting only the carrier leak component, using a narrow-band filter center angular frequency omega _c, of y (t), the component of the angular frequency omega _c Only detect.

However, when the filter band is extremely narrow,
Even when the error between the center frequency of the filter and the frequency of the local oscillator is small, the detected value greatly differs from the magnitude of the carrier leak component.

To prevent this, if the band of the filter is widened to some extent, the signal components included in the band are also regarded as carrier leaks and are canceled out.

That is, the signal component is also regarded as a carrier component, and a signal having a magnitude other than the original carrier leak is detected. For this reason, a carrier leak remains.

For the above reasons, the conventional technology is effective at the time of system startup or adjustment at the time of shipment, but is applicable to a system in which the amplitude of a signal changes or a disturbance such as a temperature fluctuation. Can not.

[0019]

FIG. 1 is a diagram showing a carrier leakage cancellation amount with respect to a cancel signal level and a phase error by a rising line, and FIG. 2 is a diagram showing a carrier leak cancellation amount with respect to the cancellation signal level and a phase error. 3
It is the figure shown dimensionally.

FIG. 3 is a graph showing the logarithmic value of the amount of carrier leak cancellation with respect to the level of the cancel signal and the phase error by a rising line. FIG. It is the figure which showed numerical value in three dimensions.

Here, the first aspect of the present invention provides a local oscillation means for dividing the generated carrier output into two and outputting the divided carrier output.
Quadrature modulating means for quadrature modulating the input baseband signal using the carrier output of the above, a phase / amplitude controlling means for controlling the phase and amplitude of the second carrier output, an output of the quadrature modulating means, In a carrier leak suppression feedback circuit having an adding means for adding an output of an amplitude control means, first and second detecting means for detecting output levels of quadrature modulation means appearing on an input side and an output side of the adding means, respectively.
And a subtraction means for obtaining a difference between the detection levels detected by the first and second level detection means.

The phase and the amplitude of the second carrier output are controlled so that the output of the subtracting means is maximized.

According to a second aspect of the present invention, in the carrier leak suppression feedback circuit, switching / level detecting means for alternately detecting the output level of the quadrature modulating means appearing on the input side and the output side of the adding means, The input quadrature modulation is performed so that the output level of the input quadrature modulation means detected by the subtraction means and the switching / level detection means is applied to the subtraction means at the same timing as the output level of the output quadrature modulation means. And delay means for delaying the output of the means.

According to a third aspect of the present invention, an analog / digital conversion means is provided between the first and second level detection means and the subtraction means.

The output of the first and second level detecting means is subtracted by digital data.

According to a fourth aspect of the present invention, a first switch is provided between the adding means and the phase / amplitude controlling means, and an offset setting section is connected to the second level detecting means.

If the first and second level detecting means do not show the same output when the first switch is opened, the offset setting unit sets the first and second level detecting means to the same level. The second level detecting means can be adjusted so that the outputs are equal to each other.

According to a fifth aspect of the present invention, in the carrier leak suppressing feedback circuit according to the fourth aspect, a comparing means for comparing the output of the first level detecting means with a reference voltage, and a circuit between the subtracting means and the offset setting section. A second switch is provided for each. When the comparator detects that the output of the quadrature modulator is larger than the reference voltage, the comparator turns off the first switch and turns on the second switch;
The offset setting unit holds the output of the subtraction means via the second switch which has been turned on, but when the second switch has been turned off, outputs the held output of the subtraction means to the second switch. The voltage is applied as an offset value of the level detection means.

Now, in order to minimize the carrier leak, the variable attenuator attenuation ratio C and the phase shifter error ψ are changed.
What is necessary is to minimize the first term on the right side of the equation (3).

That is, the magnitude of the suppressed carrier leak is given by E (D, ψ) = (D ² −2Dcosψ + 1) ^1/2 (4) where the amplitude of the quadrature modulator alone is 1. Try to minimize it.

[0031] Here, E (D, ψ) < 1 and will ^{the, D 2 - 2Dcosψ + 1 <} 1 Note, D ≧ 0, from -1 ≦ cosψ ≦ 1 cosψ> D / 2 Now, ∴ cosψ ≧ 0, 0 ≦ D ≦ 2∴−π ≦ cosψ ≦ π, 0 ≦ D ≦ 2 (5) That is, it is necessary to satisfy both of the expressions (5).

Here, a mountain-shaped region (excluding the white portion at the center) between the two b-arrows in FIG. 1 is a region satisfying the expression (5), that is, a region for canceling carrier leak.
As we approach the area of D = (0.5 to 1.5) (the white part in the center),
This indicates that the carrier leak is quickly canceled.

FIG. 2 shows the contour lines shown in FIG. 1 in a three-dimensional graph. In FIGS. 3 and 4, the black region is a region where carrier leakage increases, and the region other than this region is a black region.
The region satisfying the expression (5) is shown.

If C and ψ are controlled within the range of equation (5) with E (D, ψ) = 0 as the target value, the carrier leak can be reduced or eliminated, but the magnitude of E (D, ψ) can be reduced. Directly becomes impossible when ω = 0.

Therefore, the difference between the amplitudes of x (t) and y (t) | x (t) | − | y (t) | = A [1- (D ² −2Dcoss + 1) ^1/2 ] If (6) is detected and the detected value is set to A, that is, the maximum value, equation (4) necessarily becomes minimum.

As described above, the present invention makes it possible to determine C and ψ
The amplitude of x (t) is subtracted from the amplitude of y (t), and the result is monitored to maximize it.

That is, in the present invention, the difference between the output x (t) of the quadrature modulator and the output y (t) after the synthesis of the carrier cancel signal is monitored and feedback is performed.

Monitoring this difference is equivalent to directly monitoring the carrier leak. Therefore, the quadrature modulation output can be obtained even for disturbances such as temperature fluctuations and a system in which the baseband signal changes. Can be reduced or offset.

[0039]

FIG. 5 is a block diagram of a main part of a first embodiment of the present invention, FIG. 6 is a block diagram of a main part of another embodiment of the first invention, and FIG. FIG. 8 is a main part configuration diagram of a third embodiment of the present invention, FIG. 9 is a main part configuration diagram of a fourth embodiment of the present invention, and FIG. FIG. 3 is a configuration diagram of a main part of an embodiment of the present invention.

Here, 1 is a quadrature modulator, 2 is a local oscillator, 3 is a 180-degree phase shifter, 4 is a level adjuster,
Reference numerals 5 and 6 are level detectors, 7 is an adder, 8 is a subtractor, 9 is a gain setting unit, 10 is a phase setting unit, and 12 is a differential amplifier.

Further, 201 is a switch, 202 is a level detector, 203 is a delay unit, and 301 and 302 are analog / digital converters.
Digital converter 401, offset setting unit 402
Is a switch, 403 is a voltmeter, 501 is a comparator, 50
Reference numerals 2 and 503 indicate switches.

Further, the phase / amplitude control means in claim 1 comprises a phase shifter 3, a level adjuster 4, a gain setting section 9, and a phase setting section 10, and the switching / level detection means in claim 3 Is composed of a switch 201 and a level detector 202. The analog / digital conversion means in claim 4
/ D301, / 302.

The operation of FIGS. 5 to 11 will be described below.

In FIG. 5, the carrier output of the local oscillator 2 is distributed.
To the phase shifter 3.

Then, the quadrature modulator 1 quadrature-modulates the input I-channel and Q-channel baseband signals, and sends the resultant to the adder 7 as the output of the quadrature modulator.

The 180-degree phase shifter 3 shifts the phase of the added carrier output (hereinafter, referred to as a carrier cancel signal) by 180 degrees and sends it to the level adjuster 4.
The level adjuster 4 adjusts the level and sends it to the adder 7 as an output of the level adjuster.

Therefore, the adder 7 combines the carrier cancel signal sent from the level adjuster 4 with the output of the quadrature modulator, and sends it as a combined output.

Here, the level detector 5 indicates the level of the output of the quadrature modulator, the level detector 6 indicates the level of the combined output,
Although each of them is detected, these outputs contain modulated signal components of the same level and carrier leaks of different levels.

The subtractor 8 subtracts the detection outputs of the level detectors 5 and 6 so that the modulation signal component becomes 0, and only the difference of the carrier leak necessary for the control is used as the subtractor output as the gain setting section 9 and the phase setting section 10. Add to

Therefore, the gain setting unit and the phase setting unit adjust the 180-degree phase shifter 3 and the level adjuster 4 so that the output of the subtractor becomes the maximum level. As a result, the modulated signal from which the carrier leak has been canceled is transmitted.

In FIG. 6, the I-channel signal, the Q-channel signal, and the carrier output of the local oscillator 2 are input to the quadrature modulator 1 at predetermined levels, respectively, and become quadrature-modulated outputs.

On the other hand, the 180-degree phase shifter 3 shifts the phase of the distributed carrier cancel signal by 180 degrees.

Further, the level adjuster 4 adjusts the level of the carrier cancel signal output from the 180-degree phase shifter 3 to a signal level that can cancel (or greatly reduce) carrier leak.

The adder 7 cancels the carrier leak by adding the output of the level adjuster 4 to the output of the quadrature modulator 1.

The level detector 5 detects the level of the quadrature modulation output which is the output of the quadrature modulator 1.

The level detector 6 detects the level of the quadrature modulation output from which the carrier leak output from the adder 7 has been canceled.

The differential amplifier 12 amplifies the difference between the outputs of the level detectors 5 and 6, and outputs a positive value when the output of the level detector 5 is larger and a negative value when the output is opposite.

The gain setting section 9 monitors the output of the differential amplifier, and changes the gain in the same direction as the previous time while the output is increasing, and in the opposite direction to the previous time when the output decreases. The level adjuster 4 is controlled so as to perform the adjustment.

At this time, if the increase or decrease of the output of the differential amplifier 12 continuously changes, it is considered that the output has converged.

The phase setting unit 10 monitors the output of the differential amplifier 12, and when the output is increasing, the phase is set in the same direction as the previous time, and when the output is reduced, the phase is set in the direction opposite to the previous time. The 180-degree phase shifter 3 is controlled to change.

At this time, if the increase or decrease of the output of the differential amplifier 12 continuously changes, it is considered that the output has converged.

When one of the gain setting unit 9 and the phase setting unit 10 is operating, the other operation stops, and the setting unit that operates is switched every time the operation converges.

In FIG. 7, a single level detector 202
Switches the output of the quadrature modulator 1 and the output of the adder 7 with a switch 2
01, the detection result is delayed by the delay unit 203 and the detection result is input to the subtracter 8 without delay.

The delay unit 203 gives the output of the quadrature modulator 1 a delay amount to be applied to the subtractor 8 simultaneously with the output of the adder 7.

The gain setting section 9 and the phase setting section 10 operate only when the switch 201 is connected to the quadrature modulator 1 side or the adder 7 side.

As described above, by using a single level detector, errors in the detection values of the level detectors 5 and 6 in FIG. 6 are absorbed.

Other operations are the same as the circuit operation of the first embodiment of the present invention.

In FIG. 8, after the outputs of the level detectors 5 and 6 are converted into digital data by the corresponding A / D converters 301 and 302, the outputs of both are subtracted by the subtractor 8.

With such a configuration, an error in the subtraction value due to the drift current or the like of the differential amplifier 12 in FIG. 6 can be absorbed.

The other operation is the same as the circuit operation of the first embodiment of the present invention.

In FIG. 9, while the input to the adder 7 is cut off by the switch 402, the outputs of the level detectors 5 and 6 are monitored by the voltmeter 403, and the outputs of the level detectors 5 and 6 become equal. Offset setting section 40
Adjust 1

By this initial adjustment, if the adder 7 has a loss, this is corrected.

When the system performs a normal operation,
The switch 402 is turned on. Other operations are the same as the circuit operation of the first embodiment of the present invention.

In FIG. 10, the comparator 501 compares the output of the level detector 5 with the reference voltage V _0, and switches 502 and 503 are turned on / off according to the comparison result.

The operation of the switch is such that the switch 502 is turned off when the output of the quadrature modulator 1 becomes larger than the reference value.

Reference value V ₀ to be compared by comparator 501
Is previously adjusted to the value of the level detector 5 when the output of the quadrature modulator 1 is large enough to ignore the carrier leak.

The offset setting unit 401 includes a switch 50
The output of the subtractor 8 when the switch 3 is closed is held, and this is used as the offset value when the switch 503 is off.

By this operation, when the adder 7 has a loss, and when the loss fluctuates, this is corrected.

The other operations are the same as the circuit operation of the first embodiment of the present invention.

[0080]

According to the present invention, the magnitude of the carrier leak is detected for extracting the carrier cancel signal from the carrier signal and automatically adjusting the level or the gain so that the carrier leak is canceled or reduced. It can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing the amount of cancellation of a carrier leak with respect to the level of a cancellation signal and a phase error by a rising line.

FIG. 2 is a diagram three-dimensionally illustrating a carrier signal cancellation amount with respect to a cancellation signal level and a phase error.

FIG. 3 is a diagram illustrating logarithmic values of the amount of cancellation of carrier leak with respect to the level and phase error of a cancel signal by a rising line.

FIG. 4 is a diagram three-dimensionally showing a logarithmic value of a cancel amount of a carrier leak with respect to a level and a phase error of a cancel signal.

FIG. 5 is a configuration diagram of a main part of the first embodiment of the present invention.

FIG. 6 is a configuration diagram of a main part of another embodiment of the first invention.

FIG. 7 is a configuration diagram of a main part of a second embodiment of the present invention.

FIG. 8 is a configuration diagram of a main part of a third embodiment of the present invention.

FIG. 9 is a configuration diagram of a main part of a fourth embodiment of the present invention.

FIG. 10 is a configuration diagram of a main part of a fifth embodiment of the present invention.

FIG. 11 shows an example of a configuration diagram of a main part of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quadrature modulator 2 Local oscillator 3 180-degree phase shifter 4 Level adjuster 5, 6 Level detector 7 Adder 8 Subtractor 9 Gain setting unit 10 Phase setting unit 12 Differential amplifier 100 90-degree phase shifter 101, 102 Multiplier 103 Adder 201 Switch 202 Level detector 203 Delayer 301, 302 Analog / Digital converter 401 Offset setting unit 402 Switch 403 Voltmeter 501 Comparator 502, 503 Switch

Claims (5)

[Claims] 1. A local oscillator for dividing a generated carrier output into two, outputting the divided carrier output, an orthogonal modulator for orthogonally modulating an input baseband signal using the first carrier output, and a second carrier output. Phase / amplitude control means for controlling the phase and amplitude, the output of the quadrature modulation means and the phase / amplitude control means,
In a carrier leak suppression feedback circuit having an adding means for adding an output of an amplitude control means, a first and a second level detecting means for detecting output levels of a quadrature modulation means appearing on an input side and an output side of the adding means, respectively. Means, and first and second level detection means, respectively provided with subtraction means for obtaining a difference between the detected detection levels, and the phase of the second carrier output is set so that the output of the subtraction means becomes maximum. A carrier leak suppression feedback circuit having a configuration for controlling the amplitude and the amplitude. 2. The carrier leak suppression feedback circuit, wherein: a switching / level detecting means for alternately switching and detecting an output level of a quadrature modulating means appearing on an input side and an output side of the adding means; The output of the input quadrature modulator is delayed so that the output level of the input quadrature modulator detected by the switching / level detector is applied to the subtractor at the same timing as the output level of the output quadrature modulator. 2. The carrier leak suppression feedback circuit according to claim 1, wherein a delay means for performing the delay is provided. 3. An analog / digital converter between said first and second level detecting means and said subtracting means.
2. The carrier leak suppression feedback circuit according to claim 1, further comprising a digital conversion unit, wherein an output of the first and second level detection units is subtracted by digital data. 4. A first switch is provided between the adding means and the phase / amplitude control means, an offset setting section is connected to the second level detecting means, and the first switch is opened. When the first and second level detecting means do not show the same output, the second level detecting means is controlled by the offset setting unit so that the outputs of the first and second level detecting means are equal to each other. The carrier leak suppression feedback circuit according to claim 1, characterized in that the carrier leakage suppression circuit is configured to be able to adjust. 5. The carrier leak suppression feedback circuit according to claim 4, wherein: a comparing means for comparing an output of said first level detecting means with a reference voltage; and a second switch between said subtracting means and an offset setting section. The comparing means, when detecting that the output of the quadrature modulating means is larger than the reference voltage, turns off the first switch, turns on the second switch, and turns off the offset setting section. The output of the subtraction means is held via the second switch in the state, but when the second switch is turned off, the held output of the subtraction means is offset by the second level detection means. A carrier leak suppression feedback circuit characterized in that it can be applied as a value.