JP2852292B2 - Carrier leak compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a carrier leak compensation circuit for reducing the influence of carrier leak occurring in a transmitter used in a spread spectrum communication system (hereinafter referred to as a CDMA system).

[0002]

2. Description of the Related Art In a transmitter used in a CDMA system, there are two main causes of carrier wave leakage. One is the generation of unnecessary vector components on the I / Q plane due to the influence of the DC offset voltage of each of the primary and secondary modulated baseband signals I and Q, and the other is the quadrature modulation. This is the presence of local leak that occurs because part of the local signal input to the device leaks to the high frequency circuit (RF) side.

On the other hand, a carrier leak suppressing method for reducing the influence of carrier wave leakage as described above is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 6-303145. This is because the quadrature modulation signal output from the quadrature modulator is demodulated into baseband signals I and Q, and the baseband signals I and Q are demodulated.
Each DC component in Q is fed back to the input side of the quadrature modulation unit, and loop control is performed on the output side of the quadrature modulation unit so that the DC component is eliminated, so that the digital signals of the baseband signals I and Q are converted. This is to suppress carrier wave leakage generated by a DC component generated when each is converted into an analog signal.

[0004]

However, in such a conventional carrier leak suppressing method, a carrier leak is caused by a local leak in which a part of a local signal input to the quadrature modulator leaks to the RF side. There is a problem that the circuit configuration cannot be suppressed because it cannot be suppressed and a demodulation unit for returning the quadrature modulated signal to the baseband signals I and Q must be provided. Furthermore, since the output power from the transmitter used in the CDMA system changes according to the number of multiplexed channels, when the number of multiplexed channels is large, the influence of carrier leak can be ignored, but the number of multiplexed channels is small. When the amount is small, the output power is small, so that the ratio to the carrier leak is deteriorated, and the modulation accuracy and the inter-symbol interference are deteriorated.

The present invention has been made to solve the above-mentioned problem. With a simple circuit configuration, when the number of multiplexed channels is small, that is, when the output power is small, the baseband signal is converted to the maximum number of multiplexed channels. Amplify to the level of the time, and attenuate the amount of amplification level with a high-frequency signal to improve the ratio of output power to carrier leak to the same level as at the maximum channel multiplex number while maintaining output power. It is an object of the present invention to obtain a carrier leak compensation circuit capable of performing the above.

[0006]

To achieve the above object,
2. The carrier leak compensation circuit according to claim 1, wherein the arithmetic unit outputs a first baseband signal I and a first baseband signal Q subjected to primary modulation and secondary modulation, and the first baseband signal A first digital / analog converter for converting I from a digital signal to an analog signal, a second digital / analog converter for converting the first baseband signal Q from a digital signal to an analog signal, and the first digital / analog converter. A first baseband amplifier for amplifying a second baseband signal I output from an analog converter to a value specified by a first digital control signal of the arithmetic unit, and a second digital / analog converter. The output second baseband signal Q is amplified to a value specified by a first digital control signal of the arithmetic unit. 2 baseband amplifiers, a third baseband signal I amplified by the first baseband amplifier and a third baseband signal Q amplified by the second baseband amplifier, and a local signal Modulator for quadrature-modulating a signal, a local oscillator for inputting the local signal to the quadrature modulator, and a third digital / analog for converting a second digital control signal output from the arithmetic unit to an analog control signal A converter and a variable attenuator that attenuates the first high-frequency signal output from the quadrature modulator to a value specified by the analog control signal, and converts the second high-frequency signal output from the variable attenuator to a high-frequency signal. It is designed to be amplified by an amplification unit.

The carrier leak compensating circuit according to a second aspect of the present invention is configured such that the arithmetic unit receives output power information according to the number of multiplexed channels from an external circuit and receives the first base in accordance with the output power information. It has a function of controlling the amplification degree of the band amplifier and the second baseband amplifier and controlling the attenuation of the variable attenuator according to the output power information.

Further, the carrier leak compensation circuit according to the invention of claim 3 is arranged such that the first baseband amplifier and the second baseband amplifier receive the first digital control signal output from the operation unit. It has a function of amplifying the second baseband signal I and the second baseband signal Q uniformly and simultaneously up to the level of the maximum number of multiplexed channels.

The carrier leak compensation circuit according to a fourth aspect of the present invention provides the carrier attenuator wherein the first high-frequency signal is set to a level designated by the analog control signal supplied from the third digital / analog converter to the variable attenuator. It has a function of damping.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a first baseband signal I which is primary-modulated and
The arithmetic unit outputs a baseband signal Q. The arithmetic unit includes hardware and a processor that perform a product-sum operation using a multiplier and an adder. The first baseband signal I is a first digital / analog (hereinafter, referred to as D / A)
The converter 2 converts the digital signal into an analog signal. The first baseband signal Q is the second D / A
The digital signal is converted into an analog signal by the converter 3. The first D / A converter 2 and the second D / A converter 3 are described in “Analog Devices Data Book”, 1995/1996,
It can be easily realized by a D / A converter represented by AD9713B described in P4-537 to P548. Reference numeral 4 denotes a first baseband amplifier for amplifying the second baseband signal I output from the first D / A converter 2;
Is a second baseband amplifier for amplifying the second baseband signal Q output from the second D / A converter 3.

Here, the gain of each of the baseband amplifiers 4 and 5 is controlled by the arithmetic unit 1 so that the second baseband signal I and the second baseband signal Q are respectively supplied to the level when the maximum number of channels is multiplexed. Amplify with high accuracy up to
It outputs a third baseband signal I and a third baseband signal Q. 6 is a quadrature modulator that receives these third baseband signal I and third baseband signal Q and quadrature modulates a local signal, 7 is a local oscillator that outputs the local signal, and 8 is a quadrature modulator 6
Is a variable attenuator that attenuates the first high-frequency signal modulated by the above to a level specified by an analog control signal provided via a third D / A converter 9 and outputs the same as a second high-frequency signal. Reference numeral 10 denotes a high-frequency amplifier that amplifies the second high-frequency signal and outputs the second high-frequency signal to the output terminal 11 with specified output power.

FIG. 2 shows a specific example of the first baseband amplifier 4 and the second baseband amplifier 5. Since the first baseband amplifier 4 and the second baseband amplifier 5 use the same circuit and operate the same, the first baseband amplifier 4 will be described. Here, a case where the first baseband amplifier 4 is a non-inverting amplifier circuit will be described. 12 is a non-inverting input terminal 1
3 is an operational amplifier to which the second baseband signal I is input, and the second baseband signal I is
And output to the baseband output terminal 14. A variable resistor 16 is connected between the inverting input terminal 15 of the operational amplifier 12 and the baseband output terminal 14. Further, the inverting input terminal 15 is connected to the ground via the resistor 17. The third baseband signal I output from the baseband output terminal 14 is negatively fed back to the inverted input terminal 15 through the variable resistor 16. The amplification degree of the operational amplifier 12 is
It can be varied by changing the resistance value of the variable resistor 16.

FIG. 3 shows a simple concrete example of the variable resistor 16. The variable resistor 16 includes a switch 18 and resistors 19-1 to 19-8. The input terminal of the resistor 19 is connected to the output terminal 14, and the other terminal is connected to the input terminal of the switch 18. The other output terminal of the switch 18 is connected to the inverting input terminal 15. The switch 18 is turned on / off by a digital control signal of the operation unit 1. As a specific example of the switch 18, there is a multiplexer represented by, for example, μPD4051B (NEC Corporation). When this multiplexer is used, eight kinds of resistance values can be realized by a 3-bit digital control signal from the arithmetic unit 1. FIG. 3 shows a case where eight kinds of resistance values are realized.

A part of the local signal output from the local oscillator 7 leaks to the high frequency circuit side, so that a constant level of local leak always exists.
The variable attenuator 8 is the first attenuator output from the quadrature modulator 6.
Is attenuated by the amount amplified by the first baseband amplifier 4. At this time, the first high-frequency signal and the carrier leak are simultaneously attenuated at the same level by the variable attenuator 8, so that the ratio between the second high-frequency signal output from the variable attenuator 8 and the carrier leak does not deteriorate. Since the second high-frequency signal and the carrier leak are simultaneously amplified by the high-frequency amplifier 10 at the same level, the ratio between the third high-frequency signal output from the high-frequency amplifier 10 and the carrier leak can be specified without deteriorating. The output power thus output can be output.

Here, the third D / A converter 9 is described in "NEC General-purpose Linear IC Data Book", P692.
It can be easily realized by a D / A converter represented by μPD6376 described in P704. The variable attenuator 8 is
"'94 .8 Hitachi Diode Catalog", P572
To P573, it can be easily realized by using a PIN diode represented by HVM14S.

Next, the operation will be described. First, the first baseband signal I output from the arithmetic unit 1 is the first D / A
The converter 2 converts the digital signal into a second baseband signal I of an analog signal, and the second baseband signal I is amplified by the first baseband amplifier 4 to a level at the time of the maximum number of multiplexed channels. . Similarly, the first baseband signal Q is converted from a digital signal to a second baseband signal Q of an analog signal by the second D / A converter 3, and the second baseband signal Q is converted to the second baseband signal Q. The signal is amplified to the level at the time of the maximum number of multiplexed channels by the two baseband amplifiers 5. The first
Since the same circuit is used for the baseband amplifier 4 and the second baseband amplifier 5 and the operation is the same as described above, here, the switch 18 of the μPD4051B is connected using the first baseband amplifier 4. The operation when used will be described for the case where the maximum number of multiplexed channels is eight.

The arithmetic unit 1 obtains information of a level to be output from the output terminal 11 according to the number of multiplexed channels (hereinafter referred to as output level information) from an external circuit. Output terminal 11
Between the output power output from the
As shown in FIG. 4, there is a 1: 1 relationship. Furthermore, since there is a 1: 1 relationship between the output level information and the number of multiplexed channels as shown in FIG. 5, the operation unit 1 only needs to obtain the output level information. In order to always output the level at the time of the maximum number of multiplexed channels from the baseband output terminal 14, the arithmetic unit 1 determines the relationship between the output level information and the amplification factor of the first baseband amplifier 4 as shown in FIG. It is stored as a data table.

When obtaining the output level information, the arithmetic unit 1 sets the amplification of the first baseband amplifier 4 according to FIG. For example, when the arithmetic unit 1 obtains the output level information of VI, the gain of the first baseband amplifier 4 is set to GI, so that the output level information and the resistance value 1 shown in FIG.
The resistor 19-1 is turned on in accordance with the relationship with 9-1 to 19-8. Therefore, the first baseband output terminal 14
The third baseband signal I output from the first baseband amplifier 4 is negatively fed back to the inverting input terminal 15 through the conductive resistor 19-1, the amplification of the first baseband amplifier 4 becomes G1, and the third baseband signal I Is the level when the maximum number of channels is multiplexed. In addition, the calculation unit 1
When the output level information of 8 is obtained, the amplification of the first baseband amplifier 4 is set to G8, so that the resistor 19-8 is turned on according to FIG. Therefore, the third baseband signal I output from the baseband output terminal 14 is negatively fed back to the inverting input terminal 5 through the conductive resistor 9-8, so that the amplification degree of the first baseband amplifier 4 is increased. G8, and the third baseband signal I
Is the level when the maximum number of channels is multiplexed. In FIG. 7, “1” indicates that the resistor is ON, and “0” indicates that the resistor is OFF.
Is shown.

In this manner, the third baseband signal I and the third baseband signal I, which are uniformly and simultaneously amplified by the first baseband amplifier 4 and the second baseband amplifier 5,
Is input to the quadrature modulator 6 at the same time to quadrature modulate the local signal. A local oscillator 7 is connected to the quadrature modulator 6.
Is leaked to the RF side, so that a constant level of local leak always exists. The causes of the carrier wave leakage include the generation of unnecessary vector components on the I / Q plane due to the influence of the DC offset voltage of each of the first baseband signal I and the first baseband signal Q, as described above. There are two effects of local leaks. For example, the first baseband amplifier 4 and the second baseband amplifier 5
Of the first baseband signal I and the first baseband signal Q, the influence of unnecessary vector components on the I / Q plane due to the DC offset voltage of each of the first baseband signal I and the first baseband signal Q can be reduced. In this case, the influence of the local leak, which always occurs at a constant level, is dominant.

As described above, between the third baseband signal I and the third baseband signal Q output from the first baseband amplifier 4 and the second baseband amplifier 5, and the number of multiplexed channels. Has a 1: 1 relationship, and when the number of multiplexed channels is large, for example, FIG.
As shown in (a), at the maximum number of multiplexed channels, the levels of the third baseband signal I and the third baseband signal Q are large, and the first high-frequency signal output from the quadrature modulator 6 and the carrier leak , The effect of carrier leak can be neglected. But,
When the number of multiplexed channels is small, the levels of the third baseband signal I and the third baseband signal Q are small, so that the ratio between the first high-frequency signal output from the quadrature modulator 6 and the carrier leak is reduced. −ydB, and the influence of carrier leak cannot be ignored. However,
According to the present invention, as shown in FIG. 8B, the third baseband signal I and the third baseband signal Q are always at the level -xdB at the time of the maximum number of multiplexed channels.
The first high-frequency signal is also always at the level when the maximum number of channels is multiplexed, and the ratio between the first high-frequency signal and the carrier leak is equal to the level at the maximum number of multiplexes regardless of the number of multiplexed channels. xdB is maintained.

On the other hand, the quadrature-modulated first high-frequency signal is amplified in baseband by a variable attenuator 8 whose attenuation can be controlled by an analog control signal output from a third D / A converter 9. Attenuated. The attenuation of the variable attenuator 8 and the first baseband amplifier 4 and the second
There is a 1: 1 relationship between the amplification degree of the baseband amplifier 5 and the arithmetic unit 1 as shown in FIG. The above relationship with the amplification degree of the baseband amplifier 5 is held as a data table.

That is, when the amplification degree of the first baseband amplifier 4 and the second baseband amplifier 5 is G1, the analog control signal output from the third D / A converter 9 according to FIG. The attenuation of the variable attenuator 8 becomes A1, and the first high-frequency signal is attenuated by A1.
Similarly, when the amplification degree of the first baseband amplifier 4 and the second baseband amplifier 5 is G8, the analog control signal output from the third D / A converter 9 according to FIG. The attenuation of the attenuator 8 becomes A8, and the first high-frequency signal is attenuated by A8. At this time, since the first high-frequency signal and the carrier leak are simultaneously attenuated at the same level, the ratio between the second high-frequency signal output from the variable attenuator 8 and the carrier leak does not deteriorate. The high-frequency signal is amplified by the high-frequency amplifier 10. The second high-frequency signal and the carrier leak are transmitted to the high-frequency
Since the signals are amplified at the same level by 0 at the same time, as a result, the ratio between the third high-frequency signal amplified by the high-frequency amplifier 10 and the carrier leak does not deteriorate. According to the above operation, the ratio between the output power and the carrier leak can be improved to the same level as the case of the maximum number of multiplexed channels while maintaining the specified output power.

[0023]

As described above, according to the carrier leak compensating circuit of the present invention, when the number of multiplexed channels is small, that is, when the output power is small, the baseband signal is transmitted when the number of multiplexed channels is the maximum. By amplifying the level to the level and attenuating the amount of the amplified level with a high-frequency signal, the output power and the carrier leak ratio are improved to the same level as when the maximum number of channels is multiplexed, while maintaining the specified output power. As a result, it is possible to obtain an effect that deterioration of modulation accuracy and intersymbol interference can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a carrier leak compensation circuit of the present invention.

FIG. 2 is a circuit diagram showing an internal configuration of first and second baseband amplifiers in FIG.

FIG. 3 is a circuit diagram showing an internal configuration of a variable resistor in FIG.

FIG. 4 is an explanatory diagram showing the relationship between the number of multiplexed channels and output power in the present invention.

FIG. 5 is an explanatory diagram showing a relationship between the number of multiplexed channels and output level information in the present invention.

FIG. 6 is an explanatory diagram showing the relationship between output level information and amplification according to the present invention.

FIG. 7 is an explanatory diagram showing a relationship between output level information and a conductive resistance according to the present invention.

FIG. 8 is an explanatory diagram correspondingly explaining the relationship between the third baseband signal I and the third baseband signal Q and carrier leak in the related art and the present invention.

FIG. 9 is a diagram showing the relationship between the degree of amplification and the amount of attenuation in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Operation part 2 1st D / A converter (1st digital / analog converter) 3 2nd D / A converter (2nd digital / analog converter) 4 1st baseband amplifier 5 2nd baseband Amplifier 6 Quadrature modulator 7 Local oscillator 8 Variable attenuator 9 Third D / A converter (third digital / analog converter) 10 High-frequency amplifier 11 Output terminal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04J 13/00 H04L 27/36

Claims (4)

(57) [Claims] An arithmetic unit for outputting a first baseband signal I and a first baseband signal Q subjected to primary modulation and secondary modulation, and converting the first baseband signal I from a digital signal to an analog signal A first digital / analog converter for converting; a second digital / analog converter for converting the first baseband signal Q from a digital signal to an analog signal; and a second digital / analog converter output from the first digital / analog converter. A first baseband amplifier that amplifies the second baseband signal I to a value specified by a first digital control signal of the arithmetic unit; and a second baseband output from the second digital / analog converter. A second baseband amplifier for amplifying the signal Q to a value specified by a first digital control signal of the arithmetic unit; A quadrature modulator for simultaneously inputting a third baseband signal I amplified by a first baseband amplifier and a third baseband signal Q amplified by the second baseband amplifier and quadrature modulating a local signal; A local oscillator that inputs the local signal to the quadrature modulator; a third digital / analog converter that converts a second digital control signal output from the arithmetic unit into an analog control signal; A variable attenuator for attenuating the first high-frequency signal to be output to a value specified by the analog control signal; and a high-frequency amplifier for amplifying the second high-frequency signal output by the variable attenuator. Carrier leak compensation circuit. 2. The operation unit receives output power information according to the number of multiplexed channels from an external circuit, and amplifies the first baseband amplifier and the second baseband amplifier according to the output power information. 2. The carrier leak compensation circuit according to claim 1, further comprising a function of controlling the amount of attenuation of the variable attenuator in accordance with the output power information at the same time as controlling the attenuation. 3. The first baseband amplifier and the second baseband amplifier are configured to control the second baseband signal I and the second baseband signal by a first digital control signal output from the operation unit. 2. The carrier leak compensating circuit according to claim 1, having a function of amplifying the band signal Q uniformly and simultaneously up to the level when the maximum number of channels is multiplexed. 4. The variable attenuator has a function of attenuating a first high-frequency signal to a specified level by an analog control signal provided from the third digital / analog converter. 3. A carrier leak compensation circuit according to claim 1.