JPH07193455A - Variable attenuator - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize a variable attenuator with a wide dynamic range, fine control of attenuation, and low distortion. [Configuration] PIN diodes D1 to D4 are connected in series,
Insert in the forward direction with respect to the signal input / output path. A forward direct current IF is supplied to the diodes D1 to D4. This current IF is converted into a constant current by the constant current circuit 10 and further controlled by the control voltage Vc. The value of the current IF is also switched by the control of the multiplexer 12. Transistor T
The capacitor C2 is inserted in parallel with the load by controlling R1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an APC (automatic power control) circuit for controlling a transmission output of a radio device, and more particularly to a variable attenuator suitable for this circuit.

[0002]

2. Description of the Related Art As a method of controlling the transmission output of a radio device and compensating for the variation in gain of each circuit constituting the transmission system,
APC is known. Generally, in a digital cellular system such as a digital car telephone, a low distortion characteristic is required for the wireless telephone device. A low distortion factor is required because the digital modulation / demodulation method adopted in this type of system is π / 4DQPS.
This is because it is a method that involves amplitude fluctuations such as K. Therefore,
Low distortion characteristics are also required for APC circuits.
Furthermore, a wide dynamic range is required for APC. These requirements cannot be satisfied by the APC used in conventional analog communication. Therefore, APC using a variable attenuator as shown in FIG. 12 has been adopted in digital cellular.

The variable attenuator shown in FIG. 12 has four attenuators ATT to ATT4. ATT1 to ATT
4 are all π-type fixed attenuators, of which ATT1
ATT of 4 dB, ATT2 and ATT3 of 8 dB,
4 is a 16 dB attenuator. Also ATTA1 to ATT
Analog switches SW1 to SW4 are connected in parallel to each other. These switches SW1 to SW4
Are control signals CONT1 to CONT supplied from the outside.
Controlled by 4. As a result, as shown in the following table, the attenuation amount in steps of 4 dB is obtained in the range of 0 dB to 32 dB.

[0004]

[Table 1] Such a configuration is suitable for the specifications IS-54B and IS-55A of the digital cellular system implemented in North America. That is, in these systems, it is necessary to control the transmission output on the terminal station side in the range of 0 dB to 32 dB in 4 dB steps.

[0005]

However, in such a configuration, since the attenuation amount can be switched only in 4 dB steps, it is impossible to finely control the transmission output. In order to finely control the transmission output, it is necessary to reduce the amount of attenuation of each fixed attenuator, but with such a configuration, the overall circuit scale becomes large. Furthermore, the configuration shown in FIG. 12 requires four signal lines for transmitting the control signals CONT1 to CONT4, and the number of these signal lines increases as the number of fixed attenuators increases. .

The present invention has been made to solve the above problems, and the transmission output is delicately adjusted without increasing the circuit scale and the number of control signal lines. It is an object to provide an APC circuit that can be controlled and a variable attenuator suitable for the APC circuit. Another object of the present invention is to provide a variable attenuator having excellent linearity (low distortion characteristic) over a wide dynamic range. Another object of the present invention is to realize this variable attenuator with a smaller circuit and a smaller current consumption. It is another object of the present invention to provide a variable attenuator that is easily digitally processed and controlled by a CPU or the like.

[0007]

In order to achieve such an object, a variable attenuator according to the present invention responds to an attenuation element whose internal resistance has a current characteristic and a control signal supplied from the outside. And a current control means for variably controlling the value of the current flowing through the element, and the signal to be attenuated is supplied to the load impedance via the attenuation element.

Further, the present invention is characterized in that a plurality of the attenuating elements are provided and they are connected in series. The invention is further characterized in that the attenuating element is a PIN diode.

The present invention is also characterized in that the current control means includes a constant current circuit for drawing a current having a value corresponding to the control signal from the attenuating element. The present invention further includes a resistor provided on the path through which the constant current circuit draws a current from the attenuating element, and means for applying a voltage having a value corresponding to the voltage supplied as the control signal to the resistor. It is characterized by The present invention is characterized in that a plurality of the resistors are provided so that their resistance values are different from each other, and the constant current circuit includes means for selectively inserting the plurality of resistors in the path according to a control signal. To do.

The present invention is further characterized by comprising parallel impedance inserting means for inserting an impedance in parallel with the load impedance in accordance with the control signal. The present invention is characterized in that the parallel impedance inserting means includes a transistor that is turned on / off according to a control signal, and an element that is inserted in parallel with the load impedance when the transistor is turned on.

The invention is characterized in that it comprises an element for disconnecting the power supply and / or the current control means from the signal to be attenuated.

The APC circuit according to the present invention includes a frequency conversion unit for generating a radio frequency signal (RF signal) by frequency-converting an intermediate frequency signal (IF signal), and power amplification of the generated RF signal to an antenna. An APC circuit that is mounted on a radio device that includes an output power amplification unit and that automatically controls output power to an antenna, detects output power to the antenna, and generates a control signal based on the detected output power. And a variable attenuator according to the present invention, which is inserted between the frequency conversion unit and the power amplification unit and attenuates the RF signal according to the generated control signal.

The APC circuit according to the present invention is characterized in that the range of the value of the control signal used for controlling the variable attenuator is set to a range in which the change of the attenuation amount of the variable attenuator with respect to the control signal is small.

[0014]

In the variable attenuator according to the present invention, the value of the current flowing through the attenuation element is variably controlled by the current control means. The signal to be attenuated is supplied to the load impedance via the attenuating element. Further, the value of the current flowing through this element is controlled according to a control signal supplied from the outside. Therefore, the amount of signal attenuation determined by the internal resistance of the attenuating element and the value of the load impedance is controlled by the current control of the attenuating element. As a result, the amount of attenuation can be finely controlled over a wide dynamic range, and a variable attenuator having a good distortion characteristic can be obtained.

Further, the attenuating element can be constructed by a PIN diode or a series connection thereof, and the current control means can be constructed by a constant current circuit. Further, this constant current circuit can be configured such that a resistor is provided on the path for drawing the current from the attenuating element, and the value of the voltage applied to this resistor is controlled by the value of the voltage related to the control signal. The configuration can be further configured by using an operational amplifier or FET. Therefore, the variable attenuator according to the present invention has a simpler circuit configuration and consumes less power than a conventional variable attenuator having a large-scale circuit configuration, such as an AGC circuit, which has excellent linearity. Will be reduced.

In the present invention, in addition to the above-mentioned current control, the attenuation amount is controlled by switching the resistance value forming the constant current circuit and inserting a parallel impedance in the load impedance. That is, a plurality of resistors are provided on a path for drawing a current from the attenuating element, and these resistors are selectively inserted into the path by means of a multiplexer or the like, whereby an attenuating element, for example, a PIN diode series connection body. The value of the current flowing through the switch is switched, and thereby the amount of signal attenuation is switched. When a variable attenuator is inserted so that a transistor is turned on / off according to a control signal supplied from the outside and an element such as a capacitor is inserted in parallel with a load impedance when the transistor is turned on, The signal attenuation amount can be switched appropriately, and the control range of the signal attenuation amount is expanded.

In addition, by arranging an element such as a coil having a high impedance in the frequency band of the signal to be attenuated between the attenuation element and the power source and / or current control means, the signal to be attenuated from the power source And / or it becomes possible to interrupt the current control means in a signal manner (in a high frequency manner), and more suitable attenuation characteristics can be obtained.

Further, in the APC circuit according to the present invention, the output power from the power amplifier to the antenna is detected,
A control signal is generated based on the detected output power. This control signal is supplied to the variable attenuator according to the present invention inserted between the frequency converter and the power converter, and the variable attenuator attenuates the RF signal related to the output of the frequency converter. Generally, in a frequency conversion unit that performs frequency conversion using nonlinearity of a transistor or the like, the output level is usually 0d in order to maintain the linearity of the converted transmission signal.
The level is set to a low level of Bm or less, and therefore, by providing the variable attenuator according to the present invention on the output side of this frequency conversion unit, APC with good linearity is realized.

In the APC circuit according to the present invention, the range of the value of the control signal used for controlling the variable attenuator is
The attenuation of the variable attenuator is set to a value that causes little change with respect to the control signal. This makes it possible to accurately achieve the required attenuation amount.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a variable attenuator according to the first embodiment of the present invention.

In this embodiment, four PIN diodes D1 to D4 are connected in series in the forward direction along the signal input / output direction. That is, the anode of the diode D1 is connected to the signal input terminal via the capacitor C1, and the cathode of the diode D4 is connected to the signal output terminal via the capacitor C4. An RF signal is supplied to the signal input terminal from a circuit in the previous stage, for example, a frequency conversion unit from IF to RF, and a power amplification unit that amplifies the power of the RF signal is connected to the signal output terminal. Therefore, the signal input from the frequency conversion unit or the like is output to the power amplification unit or the like via these diodes D1 to D4. The capacitors C1 and C4
Is a coupling capacitor related to a signal input terminal or a signal output terminal and cuts a direct current.

For the diodes D1 to D4,
A forward DC current IF is supplied from the DC power supply Vcc through the coil L1. DC power supply Vcc is capacitor C
It is stabilized by 2 and is cut off from the signal input / output path at high frequency by the coil L1. On the other hand, this forward DC current IF is drawn to the ground side by the constant current circuit 10. That is, the diode D
The cathode of No. 4 is connected to the constant current circuit 10 via the coil L2. This coil L2 has a high impedance at high frequencies, like the coil L1 described above, and shuts off the constant current circuit 10 from the signal input / output path at high frequencies.

The capacitor C5 and the constant current circuit 10 are connected to one end of the coil L2. This capacitor C
Reference numeral 5 is a capacitor for stabilizing the DC voltage VD applied to the constant current circuit 10 and flowing an AC component to the ground side. Further, the constant current circuit 10 has a resistor R3. One end of this resistor R3 is grounded, and the other end is connected to the inverting input terminal of the operational amplifier A1. A control voltage Vc is externally applied to the non-inverting input terminal of the operational amplifier A1, and the output terminal of the operational amplifier A1 is F
It is connected to the ET gate. The drain and source of the FET1 are connected between one end of the coil L2 and one end of the resistor R3.

In such a circuit configuration, a voltage having the same value as the control voltage Vc appears at the inverting input terminal of the operational amplifier A1. As a result, the value of the current flowing through the resistor R3 is Vc /
It becomes R3. On the other hand, the forward voltage _Vf of the diodes D1 to D4 changes as the forward direct current IF increases as shown in FIG. Therefore, the voltage VD at the cathode of the diode D4 becomes n × VF (n is the number of PIN diodes, 4 in the figure), and it is understood that the voltage VD changes depending on Vc. In other words, since the drain-source voltage of the FET1 changes so that the forward DC current IF becomes Vc / R3, the forward DC current IF having a value corresponding to the control voltage Vc is fed from the diodes D1 to D4 to the constant current circuit. Will be pulled into 10.

The high frequency internal resistance rs of the PIN diodes D1 to D4 has the characteristics shown in FIG. 3 with respect to the forward direct current IF. That is, when the forward direct current IF increases, the high frequency internal resistance rs decreases. Assuming that the load impedance Zo is connected to the signal output terminal, the attenuation amount of the variable attenuator shown in FIG. 1 has a value represented by the following equation.

[0027]

ATT = 20log [(rs × 4) / | Zo |] (dB) When the number of PIN diodes is generally n,

ATT = 20 log [(rs × n) / | Zo |] (dB).

Therefore, the control voltage Vc in this embodiment is
The characteristics of the attenuation amount ATT (see the transistor TR1
Is off), the characteristic becomes as shown by A in FIG.

In the circuit shown in FIG.
A transistor TR1 that is on / off controlled by a control signal of R1 is provided. This transistor TR1
The emitter is grounded, and the collector is supplied with the power supply Vcc via the resistor 1 and connected to the cathode of the diode D4 via the capacitor C3. A resistor R2 is inserted in the base of the transistor TR1.

The transistor TR1 is turned on / off according to the TR1 control signal supplied to its base. When the transistor TR1 is off, the attenuation amount of the variable attenuator shown in FIG. 1 has the characteristic indicated by A in the figure as described above. On the other hand, when the transistor TR1 is turned on, the capacitor C3 is inserted in parallel with the load impedance Z0 connected to the signal output end, and as a result, the attenuation amount ATT has the content expressed by the following equation.

[0031]

[Equation 3] However, Zc3 is a capacitor c3 and a transistor TR1.
Is the signal impedance of. Therefore, the transistor T
When R1 is on, the control voltage Vc versus the attenuation amount A
The characteristic of TT is the characteristic shown by B in FIG.

As described above, in this embodiment, the attenuation amount ATT can be controlled in a variable number by the control voltage Vc, and it can be switched in two stages by the on / off control of the transistor TR1. AT
A variable attenuator capable of finely controlling T and having a wide control range is obtained.

FIG. 5 shows the configuration of a variable attenuator according to the second embodiment of the present invention. The constant current circuit 10 in this embodiment includes a resistor R3, operational amplifiers A1 and F described above.
It has a multiplexer 12 and a resistor R4 in addition to ET1. The multiplexer 12 selectively inserts one of the resistors R3 and R4 on the lead-in path of the forward direct current IF in accordance with a multiplexer control signal supplied from the outside. The value of the resistor R4 is set to be larger than the value of the resistor R3.

FIG. 6 shows the control voltage V in this embodiment.
The characteristic of c vs. attenuation ATT is shown. As shown in this figure, a relatively small resistor R3 is connected to the forward direct current I
When it is inserted in the path of F, the attenuation amount ATT becomes smaller than when the relatively large resistance R4 is inserted. this is,
This is because the value of the forward direct current IF becomes large when the resistance value inserted in the drawing path of the forward direct current IF becomes small, and as a result, the high frequency internal resistance rs of the diodes D1 to D4 becomes small. Further, as shown in this figure, the same attenuation amount is obtained when the control voltage Vc is 0 regardless of whether the resistance is R3 or R4. This is because when the control voltage Vc is 0, the forward direct current IF becomes 0 regardless of the resistance value, and the value of the high frequency internal resistance rs becomes rs0 shown in FIG.

FIG. 7 shows the configuration of a variable attenuator according to the third embodiment of the present invention. The variable attenuator shown in this figure has a configuration in which the first embodiment and the second embodiment are combined. Therefore, it is possible to carry out operations such as continuous variable control of the attenuation amount by the control voltage Vc, switching of the attenuation amount by the transistor TR1 control signal, and switching of the attenuation amount by the multiplexer 12.

FIG. 8 shows the control voltage V in this embodiment.
The characteristic of c vs. attenuation ATT is shown. In this figure, R3A shows the characteristic when the resistance of the multiplexer 12 is set to R3 by the control of the multiplexer 12 and the transistor TR1 is turned off by the TR1 control signal. Similarly, R4A has characteristics when resistance = R4 and TR1 = OFF, R3B has characteristics when resistance = R3 and TR1 = ON, and R4B has characteristics when resistance = R4 and TR1 = ON. Shows.

Further, in the figure, PL0 to PL10 are transmission output levels defined by North American digital cellular standards IS-54B and IS-55A, and correspondingly described attenuations are defined. It is a value representing the amount ATT in the unit of dBW. When the variable attenuator shown in FIG. 7 is used, as shown in this figure, the control voltage V
It is preferable to avoid a region where c is low and the attenuation amount ATT changes rapidly. By doing so, the control of the attenuation amount by the control voltage Vc can be performed relatively accurately.

FIG. 9 shows an application example of the variable attenuator according to the present invention. Shown in this figure is an APC circuit of a digital cellular radio section, and what is used as a variable attenuator is the configuration according to the third embodiment.

The variable attenuator 14 shown in this figure receives the transmission signal converted from IF to RF by the frequency conversion section 16 and outputs the attenuated signal to the power amplification section 18. The power amplifier 18 power-amplifies the RF signal supplied via the variable attenuator 14 and supplies the RF signal to an antenna (not shown). The transmission output of the power amplifier 18 is the detector 2
Detected by 0. The output of the detector 20 represents the transmission output level of the power amplifier 18, and this signal is A / D.
After being converted into digital data by the converter 22, the data is supplied to the arithmetic processing and control section 24. The arithmetic processing and control section 24 controls the control voltage V according to the supplied data.
In addition to the data related to c, the TR1 control signal and the multiplexer control signal are generated. The data relating to the control voltage Vc is converted into an analog voltage by the D / A converter 26 and then supplied to the variable attenuator 14, and the TR1 control signal and the multiplexer control signal are the transistor TR1.
Alternatively, the variable attenuator 14 is supplied from the arithmetic processing and control unit 24 for controlling the multiplexer 12. At this time, the arithmetic processing and control section 24 uses the data table showing the characteristics shown in FIG. 8 described above, and avoids the region where the attenuation amount ATT changes rapidly with respect to the change of the control voltage Vc, while avoiding the attenuation amount ATT. Control of.

FIG. 10 shows the intermodulation characteristic (IMD3) measured by the inventor. The characteristics shown in this figure were measured under the conditions shown in FIG. That is, for the variable attenuator 14 according to the third embodiment of the present invention, 836 MHz and 836.03 M are used.
The Hz signal was fed through the 3 dB attenuator 28 and the output of the variable attenuator 14 was measured by the spectrum analyzer 30. According to this measurement result, IMD3 is 60 dB or less when the input is 0 dBm or less. Variable attenuator 14
In order to maintain the linearity of the output signal, the frequency conversion unit 16 placed in front of the signal output signal at a low output level of 0 dBm or less. Therefore, the characteristic as shown in FIG. It can be said that the linearity (low distortion factor characteristic) suitable for / 4DQPSK digital modulation / demodulation is realized.

Further, in each of the above embodiments, the level is detected and controlled in the RF band, so that the circuit configuration and the board design are facilitated.

[0042]

As described above, according to the variable attenuator according to the present invention, the value of the current flowing through the attenuating element is variably controlled according to the control signal supplied from the outside, and the inside of the attenuating characteristic is controlled. Since the attenuation amount is made variable by utilizing the current characteristic of the resistor, it is possible to finely control the attenuation amount over a wide dynamic range. Further, this variable attenuator can be simply configured by using a PIN diode, a resistor, a capacitor, etc., and power consumption can be reduced. In addition, the resistance of the constant current circuit related to current control can be switched using a multiplexer or the like, or an impedance such as a capacitor can be inserted in parallel with the load impedance, so that the dynamic range can be further widened. it can. In addition, the variable attenuator according to the present invention is easy to control by a CPU or the like, and its distortion factor characteristic is also good.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a variable attenuator according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an IF vs. VF characteristic of a PIN diode.

FIG. 3 is a diagram showing IF vs. rs characteristics of a PIN diode.

FIG. 4 is a diagram showing Vc vs. attenuation ATT characteristics in the first embodiment.

FIG. 5 is a circuit diagram showing a configuration of a variable attenuator according to a second embodiment of the present invention.

FIG. 6 is a diagram showing Vc vs. attenuation ATT characteristics in the second embodiment.

FIG. 7 is a circuit diagram showing a configuration of a variable attenuator according to a third embodiment of the present invention.

FIG. 8 is a diagram showing Vc vs. attenuation ATT characteristics in the third embodiment.

FIG. 9 is a block diagram showing an application example of the present invention.

FIG. 10 is a diagram showing an effect of improving intermodulation characteristics in the present invention.

11 is a diagram showing a measurement environment for the characteristics of FIG.

FIG. 12 is a circuit diagram showing a configuration of a variable attenuator according to a conventional example.

[Explanation of symbols]

 D1 to D4 PIN diode L1, L2 coil C1 to C5 capacitor R1 to R4 resistance A1 operational amplifier 10 constant current circuit 12 multiplexer 14 variable attenuator 16 frequency conversion unit 18 power amplification unit 20 detector 22 A / D converter 24 arithmetic processing and Control unit 26 D / A converter Vc control voltage

Claims (11)

[Claims] 1. An attenuating element, the internal resistance of which has a current characteristic, and a current control means for variably controlling the value of a current flowing through the element according to a control signal supplied from the outside, to be attenuated. A variable attenuator characterized in that a signal is supplied to a load impedance via an attenuating element. 2. The variable attenuator according to claim 1, comprising a plurality of the damping elements and connecting them in series. 3. The variable attenuator according to claim 1, wherein the attenuating element is a PIN diode. 4. The variable attenuator according to claim 1, wherein the current control means includes a constant current circuit for drawing a current having a value corresponding to the control signal from the attenuating element. 5. The variable attenuator according to claim 4, wherein the constant current circuit provides a resistor provided on a path for drawing a current from the attenuating element and a voltage having a value according to a voltage supplied as a control signal. A variable attenuator comprising: a means for applying a resistance. 6. The variable attenuator according to claim 5, wherein a plurality of the resistors are provided so that their resistance values are different from each other, and a constant current circuit selectively selects the plurality of resistors according to a control signal. A variable attenuator comprising means for insertion on. 7. The variable attenuator according to claim 1, further comprising parallel impedance inserting means for inserting an impedance in parallel with the load impedance according to the control signal. 8. The variable attenuator according to claim 7, wherein the parallel impedance inserting means is turned on / off according to a control signal.
A variable attenuator comprising a transistor that is turned off and an element that is inserted in parallel with a load impedance when the transistor is turned on. 9. The variable attenuator according to claim 1, further comprising an element for cutting off the power supply and / or the current control means from a signal to be attenuated. 10. A radio device comprising: a frequency conversion unit that generates a radio frequency signal by frequency-converting an intermediate frequency signal; and a power amplification unit that amplifies the generated radio frequency signal and outputs the power to an antenna. In the APC circuit for automatically controlling the output power to the antenna, means for detecting the output power to the antenna, means for generating a control signal based on the detected output power, and between the frequency conversion unit and the power amplification unit. The radio frequency signal is attenuated according to the inserted control signal generated.
9. A variable attenuator according to any one of claims 9 to 9, and an APC circuit. 11. The APC circuit according to claim 10, wherein the range of the value of the control signal used for controlling the variable attenuator is a range in which the change of the attenuation amount of the variable attenuator with respect to the control signal is small. APC circuit.