JP5305481B2 - Signal transmission circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of harmonics while preventing an increase in current consumption. <P>SOLUTION: A signal transmission circuit includes: an oscillator for outputting a signal of a single frequency; an amplifier circuit comprising an amplification part for amplifying a signal outputted from the oscillator or a signal transmitted from the outside, and an output buffer part having a variable current unit for controlling an output current of a signal outputted from the amplification part; a saturation level control circuit which extracts, from a signal outputted from the amplifier circuit, a harmonic component of this signal and outputs a current control voltage for controlling a current of the variable current unit, on the basis of power of the extracted harmonic component; and a power supply control circuit for controlling power supplies of the oscillator and the saturation level control circuit. <P>COPYRIGHT: (C)2013,JPO&amp;INPIT

Description

  The present invention relates to a signal transmission circuit, and more particularly to a signal transmission circuit that suppresses the generation of harmonics.

  In a transmission circuit such as a transmission circuit that transmits a signal such as a radio signal, an amplifier circuit is generally provided, and the signal is amplified by this amplifier circuit and output. At this time, the signal may be distorted or saturated depending on the nonlinearity of the amplifying element used in the amplifying circuit or the amplification factor set in the amplifying circuit, and this distortion or saturation results in an integral multiple of the signal frequency. Harmonics are generated.

  When a signal is transmitted in a state where such harmonics are generated, there is a risk of signal deterioration or malfunction. In addition, in a predetermined communication standard, THD (Total Harmonic Distortion: Total Harmonic Distortion) indicating the ratio of the entire harmonic component to the fundamental component of the signal is defined, and the harmonic component is suppressed so as to satisfy this standard. There is a need. Therefore, in a normal transmission circuit, a harmonic component is removed using a filter or the like (for example, Patent Document 1).

  Recently, when a signal is transmitted, the signal is transmitted using a modulation method called OFDM (Orthogonal Frequency Division Multiplex) that modulates the transmission signal so as to be spread within a predetermined frequency band.

  Here, in the case of using OFDM, as shown in FIG. 6, the second harmonic and the third harmonic whose frequency is doubled and tripled with respect to the fundamental wave have predetermined frequency bands (hereinafter referred to as OFDM signals). If it occurs within the band), harmonics become noise components and the signal deteriorates. As a result, THD and the like deteriorate and communication quality deteriorates.

  Since this harmonic is generated in the OFDM signal band, it is difficult to remove it by a filter or the like. Therefore, normally, the generation of harmonics is suppressed. Specific methods for suppressing harmonics include, for example, adding a correction circuit to prevent signal distortion and saturation when individual differences due to device manufacturing variations or variations due to environmental condition fluctuations occur. A method of preventing signal distortion and saturation by increasing the saturation amplitude level of the amplifier circuit is conceivable.

JP 2000-101660 A

  However, the above-described conventional method has a problem in that when a correction circuit is added to suppress the generation of harmonics, the circuit configuration becomes complicated and large. Further, when the saturation amplitude level of the amplifier circuit is increased, there is a problem that current consumption increases.

  Therefore, the present invention has been made in view of the problems in the above-described conventional technology, and does not increase the complexity and size of the circuit configuration and suppress the generation of harmonics while preventing an increase in current consumption. An object of the present invention is to provide a signal transmission circuit capable of performing the above.

In order to achieve the above object, the present invention provides a signal transmission circuit that amplifies and outputs a signal transmitted from the outside, and an oscillator that outputs a signal of a single frequency, a signal output from the oscillator, or the An amplification circuit comprising an amplification unit for amplifying a signal transmitted from the outside, an output buffer unit having a variable current source for controlling an output current of the signal output from the amplification unit, and a signal output from the amplification circuit A saturation level control circuit that extracts a harmonic component of the signal and outputs a current control voltage for controlling the current of the variable current device based on the power of the extracted harmonic component; the oscillator and the saturation and a power control circuit for controlling the power level control circuit, a signal transmitted from the external is a spread signal having a predetermined frequency band, the signal output from the oscillator Wave number, and characterized in that as well as positioned on the low frequency side of the predetermined frequency band, the frequency of the second harmonic and third harmonic relative to the frequency is set to be included within said predetermined frequency band To do.

According to the present invention, since the current of the differential signal output from the signal transmission circuit is automatically adjusted based on the power of the extracted harmonic component, harmonics are prevented while preventing an increase in current consumption. Can be suppressed.
In addition, the frequency of the signal output from the oscillator is set to the low frequency side of the predetermined frequency band, and the frequency of the second harmonic and the third harmonic with respect to this frequency is set within the predetermined frequency band. By doing so, it is possible to generate a harmonic component with respect to the fundamental wave within a predetermined frequency band, so that it is possible to extract the harmonic component in the current adjustment mode.

  In the signal transmission circuit, the saturation level control circuit includes a filter unit that extracts a harmonic component of the signal output from the amplifier circuit, and a power detection unit that detects a sum of powers of the extracted harmonic components. A comparison unit that compares a voltage indicating the sum of the power detected by the power detection unit with a reference voltage with respect to the voltage, and the comparison unit outputs the current control voltage according to a comparison result. can do. As a result, it is possible to output a current control voltage based on the sum of the powers of the harmonic components existing in the predetermined frequency band.

  In the signal transmission circuit, when the voltage indicating the sum of power exceeds the reference voltage, the comparison unit increases the current of the variable current device, and the voltage indicating the sum of power is equal to or less than the reference voltage. In this case, the current control voltage for controlling the current of the variable current device can be output so as to decrease the current of the variable current device. Thereby, the current control voltage can be converged to the reference voltage, and the current of the variable current device can be appropriately controlled.

  In the signal transmission circuit, the filter unit can extract the second harmonic component and the third harmonic component of the signal output from the amplifier circuit.

  The signal transmission circuit may further include a control voltage storage circuit that stores the current control voltage. Thus, the current control voltage determined in the current adjustment mode can be supplied to the variable current device during the normal operation mode, and an appropriate current value can be set.

  In the signal transmission circuit, the signal transmitted from the outside and the signal output from the oscillator can be a differential signal.

  In the signal transmission circuit, the signal transmitted from the outside and the signal output from the oscillator can be a single-ended signal.

  As described above, according to the present invention, it is possible to suppress the generation of higher harmonics while preventing an increase in current consumption without causing a complicated circuit configuration or an increase in size.

1 is a block diagram showing a first embodiment of a signal transmission circuit according to the present invention. It is a basic diagram for demonstrating the relationship between a differential signal and a frequency band. It is a basic diagram for demonstrating the relationship between the output of a power detection part, and the electric current value of a variable current device. It is a block diagram which shows 2nd Embodiment of the signal transmission circuit concerning this invention. It is a block diagram which shows 3rd Embodiment of the signal transmission circuit concerning this invention. It is a basic diagram for demonstrating the harmonic which generate | occur | produces in an OFDM signal band.

  Next, an embodiment for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a first embodiment of a signal transmission circuit according to the present invention. This signal transmission circuit 1 includes a variable gain control amplifier circuit (VGA (Variable Gain Control Amp)) 2 and an oscillator (OSC: Osscillator) 3. , A saturation level control circuit 4, a voltage storage circuit 5, and a power supply control circuit 6. The signal transmission circuit 1 receives a differential signal (for example, an OFDM signal) such as a radio signal transmitted from the outside, amplifies the signal with a predetermined gain, and outputs the amplified signal. Further, when adjusting the output current, the signal transmission circuit 1 outputs the current of the differential signal that is output based on the power of the harmonic component whose frequency is an integral multiple of the fundamental wave of the input differential signal. Adjust the value.

  The VGA circuit 2 includes an output buffer 14 including a reference-side variable resistor 11, a feedback-side variable resistor 12, an amplifying unit (amplifier) 13, and a variable current source 15. A differential signal supplied to an input terminal is input to a predetermined signal. While amplifying with a gain, it outputs from an output terminal with a predetermined current value. The gain of the VGA circuit 2 is determined by the ratio of the resistance values of the reference-side variable resistor 11 and the feedback-side variable resistor 12, and a desired gain can be set by changing these resistance values.

  One end of the reference side variable resistor 11 is connected to the input terminal of the VGA circuit 2, and the other end is connected to the input terminal of the amplifying unit 13 and one end of the feedback side variable resistor 12. One end of the feedback side variable resistor 12 is connected to the other end of the reference side variable resistor 11 and the input terminal of the amplifying unit 13, and the other end is connected to the output terminal of the output buffer 14 and the output terminal of the VGA circuit 2. The

  The other end of the reference side variable resistor 11 and one end of the feedback side variable resistor 12 are connected to the input terminal of the amplifying unit 13, and the input terminal of the output buffer 14 is connected to the output terminal. In the amplifying unit 13, a feedback loop is formed by the feedback variable resistor 12 connected between the input terminal and the output terminal via the output buffer 14, so that the reference variable resistor 11 connected to the input terminal is formed. The input differential signal is amplified with a gain determined based on the resistance value of the feedback variable resistor 12 connected between the input terminal and the output terminal.

  The output terminal of the amplifier 13 is connected to the input terminal of the output buffer 14, and the other end of the feedback variable resistor 12 and the output terminal of the VGA circuit 2 are connected to the output terminal. The output buffer 14 outputs the input differential signal with a current value set in the variable current source 15. The variable current source 15 is connected to a voltage storage circuit 5 described later, and can set the current value of the differential signal output from the VGA circuit 2 in accordance with the current control voltage output from the voltage storage circuit 5. .

  The OSC 3 is connected to the input terminal of the VGA circuit 2 and outputs a differential signal having a predetermined power and a single frequency when the power is turned on under the control of a power control circuit 6 described later.

  The saturation level control circuit 4 is connected to the output terminal of the VGA circuit 2 and is supplied with a differential signal output from the VGA circuit 2 when the power is turned on under the control of the power supply control circuit 6. The saturation level control circuit 4 includes a filter unit 21, a power detection unit 22, and a comparison unit 23.

  The filter unit 21 is, for example, a band-pass filter (BPF), and allows only a predetermined frequency component included in the differential signal to pass by limiting a band of the differential signal supplied based on a predetermined cutoff frequency. . In this example, the frequency band is set so that the second harmonic and the third harmonic whose frequency is doubled and tripled with respect to the fundamental wave in the supplied differential signal can pass.

  The power detection unit 22 detects the power of a predetermined frequency component in the differential signal that has passed through the filter unit 21 and outputs a voltage corresponding to the detection result. For example, the power detection unit 22 detects the sum of the powers of the second harmonic and the third harmonic in the differential signal that has passed through the filter unit 21 and outputs a voltage proportional to the detected power.

  The comparison unit 23 is, for example, an operational amplifier, and includes two input terminals. The comparison unit 23 compares the voltages input to the respective input terminals, and outputs a voltage corresponding to the comparison result (hereinafter referred to as a current control voltage). The voltage output from the power detector 22 is supplied to one input terminal, and the second harmonic and the third harmonic of the voltage supplied to one input terminal are supplied to the other input terminal. A reference voltage defining the power value is supplied.

  The voltage storage circuit 5 is connected to the output terminal of the comparison unit 23 and the variable current source 15 provided in the output buffer 14 of the VGA circuit 2. The voltage storage circuit 5 stores the current control voltage output from the comparison unit 23 of the saturation level control circuit 4 in the current adjustment mode described later, and outputs the stored current control voltage in the normal operation mode described later. The voltage storage circuit 5 includes, for example, a CPU (Central Processing Unit), an A / D (Analog / Digital) conversion circuit, a D / A (Digital / Analog) conversion circuit, and the like. The configuration of the voltage storage circuit 5 is not limited to this example, and any configuration can be adopted as long as the voltage output from the saturation level control circuit 4 can be held.

  The power supply control circuit 6 controls ON / OFF of the power supply of the OSC 3 and the saturation level control circuit 4. For example, in the current adjustment mode, the OSC 3 and the saturation level control circuit 4 are turned on, and in the normal operation mode, the OSC 3 and the saturation level control circuit 4 are turned off.

  Next, the operation of the signal transmission circuit 1 having the above configuration will be described with reference to FIGS. The signal transmission circuit 1 includes a normal operation mode for amplifying and outputting a differential signal transmitted from the outside in accordance with the power ON / OFF of the OSC 3 and the saturation level control circuit 4 under the control of the power control circuit 6, and the VGA. A current adjustment mode for appropriately setting the current of the differential signal output from the circuit 2.

  In the normal operation mode, the power of the OSC 3 and the saturation level control circuit 4 is turned off under the control of the power control circuit 6, and the differential signal transmitted from the outside is input to the signal transmission circuit 1. The input differential signal is input to one end of the reference side variable resistor 11 of the VGA circuit 2 and has a predetermined gain determined by the amplifier 13 based on the resistance values of the reference side variable resistor 11 and the feedback side variable resistor 12. While being amplified, it is output at the current value set in the variable current source 15 of the output buffer 14.

  In the current adjustment mode, the power of the OSC 3 and the saturation level control circuit 4 is turned on by the control of the power control circuit 6, and a single frequency differential signal (fundamental wave) is output from the OSC 3 and supplied to the VGA circuit 2. The At this time, as shown in FIG. 2A, the frequency of the differential signal output from the OSC 3 is on the low frequency side of the OFDM signal band so that the third harmonic with respect to the fundamental wave A is within the OFDM signal band. The correct frequency is selected. The power of the differential signal output from the OSC 3 is equal to the power of the differential signal output from the VGA circuit 2 in the normal operation mode. Is selected.

  The differential signal supplied to the VGA circuit 2 is input to one end of the reference-side variable resistor 11 as in the normal operation mode, and the resistance values of the reference-side variable resistor 11 and the feedback-side variable resistor 12 are set by the amplifier 13. The signal is amplified with a predetermined gain determined based on the current value, and is output with a current value set in the variable current source 15 of the output buffer 14.

  As shown in FIG. 2B, the differential signal output from the VGA circuit 2 is amplified with the gain set in the VGA circuit 2 and a harmonic is generated. In this example, second to fourth harmonics B, C and D are generated in the OFDM signal band. In FIG. 2B, the dotted line portion of the fundamental wave A ′ indicates the power of the differential signal input to the VGA circuit 2, and the solid line portion indicates the gain amount amplified by the VGA circuit 2.

  The differential signal output from the VGA circuit 2 is supplied to the saturation level control circuit 4 and input to the filter unit 21. In the filter unit 21, a frequency band is set in advance so that only a predetermined frequency component can pass, and in this example, as shown in FIG. 2C, the second harmonics B and 3 of the differential signal. A frequency band in which only the second harmonic C can pass is set. Therefore, when the differential signal shown in FIG. 2B is input to the filter unit 21, only the second harmonic B and the third harmonic C of the differential signal pass, and the component of the fundamental wave A and other components Harmonic components and the like are removed.

  The second harmonic B and the third harmonic C of the differential signal that have passed through the filter unit 21 are input to the power detection unit 22, and the total power of the second harmonic B and the third harmonic C is detected. . Then, a voltage proportional to the total power detected is output. The voltage output from the power detection unit 22 is supplied to one input terminal of the comparison unit 23. In the comparison unit 23, the voltage based on the sum of the powers of the second harmonic B and the third harmonic C supplied to one input terminal is compared with the reference voltage supplied to the other input terminal. A current control voltage corresponding to the result is output and supplied to the voltage storage circuit 5.

  The current control voltage supplied to the voltage storage circuit 5 is output as it is during the adjustment of the output current, and is supplied to the variable current source 15 provided in the output buffer 14 of the VGA circuit 2. In the variable current source 15, the current value is set according to the current control voltage supplied via the voltage storage circuit 5.

  Here, a method for setting the current value of the differential signal output from the VGA circuit 2 will be described. If the output buffer 14 has a low driving capability and a small output current, distortion and saturation of the differential signal occur. Therefore, when the sum of the power of the second and third harmonics is large, the variable current device 15 When the total power is small, the output current is decreased.

  For example, in the signal transmission circuit 1, if the current of the differential signal output from the output buffer 14 is small and distortion or saturation occurs in the output signal, the sum of the power of the second harmonic and the third harmonic increases. The output voltage of the power detector 22 increases. Therefore, as shown in FIG. 3, the output voltage of the power detector 22 can be decreased by increasing the output current of the variable current generator 15.

  Further, if the current of the differential signal output from the output buffer 14 is large and the distortion or saturation of the output signal is reduced, the sum of the power of the second harmonic and the third harmonic is reduced. The output voltage decreases. Therefore, the output voltage of the power detector 22 can be increased by decreasing the output current of the variable current generator 15.

  In this manner, the operation of increasing / decreasing the output current from the variable current source 15 is repeated, and when the output voltage of the power detection unit 22 exceeds the reference voltage supplied to the comparison unit 23, the output current of the variable current source 15 is increased. In addition, when the output voltage of the power detection unit 22 is equal to or lower than the reference voltage, the output current of the variable current source 15 is decreased. As a result, the output voltage of the power detector 22 gradually converges to the reference voltage, and the output current of the variable current source 15 when the output voltage of the power detector 22 converges reduces the current consumption while suppressing harmonics. The output current is appropriate for minimization.

  At this time, the voltage storage circuit 5 holds the current control voltage output from the comparison unit 23 when the voltage of the power detection unit 22 converges. In the normal operation mode, the voltage storage circuit 5 supplies the held current control voltage to the variable current generator 15. As a result, the output current from the variable current source 15 becomes an optimum value, harmonics of the differential signal transmitted from the outside can be suppressed, and deterioration of communication quality can be prevented.

  As described above, according to the first embodiment, the current value of the differential signal output from the signal transmission circuit 1 is automatically adjusted based on the power value of the harmonic component generated in the OFDM signal band. Therefore, generation of higher harmonics can be suppressed while preventing an increase in current consumption.

  Next, a second embodiment of the signal transmission circuit according to the present invention will be described. FIG. 4 shows a second embodiment of the signal transmission circuit according to the present invention. This signal transmission circuit 30 is a VGA circuit 31 instead of the VGA circuit 2 of the signal transmission circuit 1 according to the first embodiment described above. It was set as the structure using. In addition, about the part which is common in 1st Embodiment mentioned above, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  The VGA circuit 31 includes a reference-side variable resistor 11, a feedback-side variable resistor 12, an amplification unit 13, and an output buffer unit 32. The output buffer unit 32 includes a differential unit 33, a load unit 34, and a variable current device 35. The differential unit 33 is configured by a pair of FETs (Field Effect Transistors), for example. The output terminal of the amplifying unit 13 is connected to the gate terminal of each FET, and the load unit 34 is connected to the drain terminal. The source terminals of the FETs are connected in common and connected to the variable current source 35. The variable current device 35 can change the current flowing through the load unit 34 in accordance with the current control voltage output from the voltage storage circuit 5.

  In the normal operation mode, a differential signal is input to the signal transmission circuit 30. The input differential signal is input to one end of the reference-side variable resistor 11 of the VGA circuit 31 and has a predetermined gain determined by the amplifier 13 based on the resistance values of the reference-side variable resistor 11 and the feedback-side variable resistor 12. While being amplified, it is output at the current value set in the variable current source 35 of the output buffer unit 32.

  In the current adjustment mode, when the power supply of the OSC 3 and the saturation level control circuit 4 is turned on by the control of the power supply control circuit 6, a single frequency differential signal is output from the OSC 3 and supplied to the VGA circuit 31. The differential signal supplied to the VGA circuit 31 is input to one end of the reference-side variable resistor 11 and has a predetermined gain determined by the amplifier 13 based on the resistance values of the reference-side variable resistor 11 and the feedback-side variable resistor 12. Amplified and output via the output buffer unit 32.

  The differential signal output from the VGA circuit 31 is supplied to the saturation level control circuit 4, and a current control voltage based on the sum of the power of the second harmonic and the third harmonic of the differential signal is output. The current control voltage output from the saturation level control circuit 4 is supplied to the variable current device 35 via the voltage storage circuit 5, and the current value is set in the variable current device 35 in accordance with the supplied current control voltage. .

  Here, for example, when the current of the variable current device 35 increases, the current flowing through the load unit 34 increases, and the amplitude of the differential signal output from the output terminal increases, so that the distortion of the differential signal decreases. The saturation level increases and the output power from the output buffer unit 32 increases. Thereby, since the harmonic component of the differential signal can be suppressed, the THD standard can be satisfied and the current consumption can be suppressed.

  As described above, according to the second embodiment, similar to the first embodiment, the differential signal output from the signal transmission circuit 30 based on the power value of the harmonic component generated in the OFDM signal band. Therefore, the generation of higher harmonics can be suppressed while preventing an increase in current consumption.

  Next, a third embodiment of the signal transmission circuit according to the present invention will be described. FIG. 5 shows a third embodiment of the signal transmission circuit according to the present invention, and the signal transmission circuit 40 is configured to be applicable to a single-ended signal instead of a differential signal. In addition, about the part which is common in 1st and 2nd embodiment mentioned above, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  The signal transmission circuit 40 includes a VGA circuit 41, OSC3, a saturation level control circuit 4, a voltage storage circuit 5, and a power supply control circuit 6. The VGA circuit 41 includes a reference side variable resistor 42, a feedback side variable resistor 43, and an amplifying unit. 44 and an output buffer unit 45. The gain of the VGA circuit 41 is determined by the ratio of the resistance values of the reference-side variable resistor 42 and the feedback-side variable resistor 43, and a desired gain can be set by changing these resistance values.

  The input terminal of the VGA circuit 41 is connected to one end of the reference side variable resistor 42, and the input terminal of the amplifier 44 and one end of the feedback side variable resistor 43 are connected to the other end. One end of the feedback side variable resistor 43 is connected to the other end of the reference side variable resistor 42 and the input terminal of the amplification unit 44, and the other end is connected to the output terminal of the output buffer unit 45 and the output terminal of the VGA circuit 41. Is done.

  The other end of the reference side variable resistor 42 and one end of the feedback side variable resistor 43 are connected to the input terminal of the amplifying unit 44, and the input terminal of the output buffer unit 45 is connected to the output terminal. The amplifying unit 44 forms a feedback loop by the feedback side variable resistor 43 connected between the input terminal and the output terminal via the output buffer unit 45, so that the reference side variable resistor connected to the input terminal 42 and the feedback variable resistor 43 connected between the input terminal and the output terminal are amplified with a gain determined based on the resistance value.

  The output buffer unit 45 includes a drive circuit 46 and a variable current device 47. The output terminal of the amplifying unit 44 is connected to the input terminal, and the other end of the feedback variable resistor 43 and the output of the VGA circuit 41 are connected to the output terminal. Terminal is connected. The variable current device 47 can change the current flowing through the drive circuit 46 in accordance with the current control voltage output from the voltage storage circuit 5.

  The drive circuit 46 is composed of, for example, a pair of FETs, and the gate terminals of the FETs are connected in common, and the input terminal of the output buffer unit 45 (the output terminal of the amplification unit 44) is connected. The source terminal of one FET and the drain terminal of the other FET are connected to each other and connected to the output terminal of the output buffer unit 45. Furthermore, the drain terminal of one FET is connected to the variable current generator 47, and the source terminal of the other FET is grounded.

  In the normal operation mode, the signal transmission circuit 40 receives a single end signal. The input single-ended signal is input to one end of the reference-side variable resistor 42 of the VGA circuit 41, and has a predetermined gain determined by the amplifier 44 based on the resistance values of the reference-side variable resistor 42 and the feedback-side variable resistor 43. While being amplified, it is output at the current value set in the variable current source 47 of the output buffer unit 45.

  In the current adjustment mode, when the power supply of the OSC 3 and the saturation level control circuit 4 is turned on by the control of the power supply control circuit 6, a single-frequency single-end signal is output from the OSC 3 and supplied to the VGA circuit 41. The single-ended signal supplied to the VGA circuit 41 is input to one end of the reference-side variable resistor 42 and has a predetermined gain determined by the amplifier 44 based on the resistance values of the reference-side variable resistor 42 and the feedback-side variable resistor 43. Amplified and output via the output buffer unit 45.

  The single end signal output from the output buffer unit 45 is supplied to the saturation level control circuit 4, and a current control voltage based on the sum of the power of the second harmonic and the third harmonic of the single end signal is output. The current control voltage output from the saturation level control circuit 4 is supplied to the variable current device 47 via the voltage storage circuit 5, and the current value is set in the variable current device 47 according to the supplied current control voltage. .

  Here, for example, when the current of the variable current device 47 increases, the current flowing through the drive circuit 46 increases, and the amplitude of the single-ended signal output from the output terminal increases, so that the distortion of the differential signal is reduced. The saturation level increases and the output power from the output buffer unit 45 increases. Thereby, since the harmonic component of the differential signal can be suppressed, the THD standard can be satisfied and the current consumption can be suppressed.

  As described above, according to the third embodiment, even if the signal transmitted from the outside is a single-ended signal, as in the first and second embodiments, harmonics generated in the OFDM signal band. Since the current value of the single-ended signal output from the signal transmission circuit 40 is automatically adjusted based on the power value of the component, the generation of harmonics can be suppressed while preventing an increase in current consumption.

  The first, second, and third embodiments of the present invention have been described above. However, the present invention is not limited to the above-described first, second, and third embodiments of the present invention, and the present invention is not limited thereto. Various modifications and applications are possible without departing from the scope of the invention.

  For example, in the above-described example, the saturation level control circuit 4 sets the band of the filter unit 21 so as to extract only the second harmonic and the third harmonic of the differential signal or the single-ended signal, and the power detection unit 22 The sum of the power of the second and third harmonics is detected, but this is not limited to this example. For example, all components other than the fundamental wave generated in the OFDM signal band may be extracted by the filter unit 21, and the power detection unit 22 may detect the total power of these extracted components.

  For example, in the above-described example, a case where a wireless signal is used as an input signal has been described. However, the present invention is not limited to this, and the same circuit configuration can be applied to wired data communication.

1, 30, 40 Signal transmission circuit 2, 31, 41 Variable gain control amplification circuit 3 Oscillator 4 Saturation level control circuit 5 Voltage storage circuit 6 Power supply control circuit 11, 42 Reference variable resistor 12, 43 Feedback variable resistor 13, 44 Amplifying unit 14 Output buffers 15, 35, 47 Variable current device 21 Filter unit 22 Power detection unit 23 Comparison unit 32, 45 Output buffer unit 33 Differential unit 34 Load unit 46 Drive circuit

Claims (7)

A signal transmission circuit that amplifies and outputs a signal transmitted from the outside,
An oscillator that outputs a single frequency signal;
An amplifying circuit comprising: an amplifying unit for amplifying a signal output from the oscillator or the signal transmitted from the outside; and an output buffer unit having a variable current device for controlling an output current of the signal output from the amplifying unit; ,
Saturation level control for extracting a harmonic component of the signal from the signal output from the amplifier circuit and outputting a current control voltage for controlling the current of the variable current device based on the power of the extracted harmonic component Circuit,
A power supply control circuit for controlling the power supply of the oscillator and the saturation level control circuit ,
The signal transmitted from the outside is a spread signal having a predetermined frequency band,
The frequency of the signal output from the oscillator is located on the low frequency side of the predetermined frequency band, and the frequencies of the second harmonic and the third harmonic with respect to the frequency are included in the predetermined frequency band. A signal transmission circuit characterized by being set as follows. The saturation level control circuit includes:
A filter unit for extracting harmonic components of the signal output from the amplifier circuit;
A power detector that detects the sum of the powers of the extracted harmonic components;
A voltage indicating the total power detected by the power detection unit, and a comparison unit that compares a reference voltage with respect to the voltage;
The signal transmission circuit according to claim 1, wherein the comparison unit outputs the current control voltage according to a comparison result.   The comparison unit increases the current of the variable current device when the voltage indicating the sum of power exceeds the reference voltage, and the variable when the voltage indicating the sum of power is equal to or less than the reference voltage. The signal transmission circuit according to claim 2, wherein the current control voltage for controlling the current of the variable current device is output so as to reduce the current of the current device.   The signal transmission circuit according to claim 2, wherein the filter unit extracts a second harmonic component and a third harmonic component of the signal output from the amplifier circuit.   The signal transmission circuit according to claim 1, further comprising a control voltage storage circuit that stores the current control voltage. Signal output from the transmitted signal and the oscillator from the outside, a signal transmission circuit according to any one of claims 1 to 5, characterized in that a differential signal. Signal output from the transmitted signal and the oscillator from the outside, a signal transmission circuit according to any one of claims 1 to 5, characterized in that a single-ended signal.

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