JP2011244139A - Frequency control circuit and output frequency control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency control circuit and an output frequency control method which prevent communication quality from being deteriorated when a ground potential is fluctuated.SOLUTION: The frequency control circuit includes a voltage control oscillator 10 which fluctuates an output frequency according to an input voltage, a phase detector 11 which detects a phase difference between the output frequency output from the voltage control oscillator 10 and a reference frequency and fluctuates an output voltage according to the phase difference, and an adder 12 which adds a potential difference caused by a resistance generated between the ground potential of the voltage control oscillator 10 and a reference ground potential of the phase detector 11 to the output voltage and outputs to the voltage control oscillator 10.

Description

  The present invention relates to a frequency control circuit and an output frequency control method, and more particularly to a frequency control circuit including a PLL circuit and an output frequency control method using the PLL circuit.

  The microwave radio communication device includes a high frequency band voltage controlled oscillator (VCO), a mixer (MIX), a power amplifier (PA) as a final transmission amplifier, an intermediate frequency band power amplifier, a power source, etc. It is comprised by the several circuit which has the function of. There are cases where some of these functions are collected and configured as several functional parts (modules).

  In this case, the ground potential (GND) between the modules is connected by connecting the modules using a connector, or by screwing the housings of the modules used as the GND. Here, an example of a microwave radio communication apparatus is shown using FIG.

  The microwave radio communication apparatus of FIG. 4 includes a high frequency band module 110 configured using a VCO 120, a transmission MIX 130, a reception MIX 140, a PA 150, and a low noise amplifier (LNA) 160 that is a reception first stage amplifier. I have. The microwave radio communication apparatus further includes a module 210 configured using an intermediate frequency band amplifier 220, an intermediate frequency band amplifier 230, a power supply circuit 240, and a PLL circuit 250.

  Signals or power supply between the module 110 and the module 210 are input / output using a connector. Since the high frequency band module 110 handles high frequency signals, the substrate used is a high frequency substrate. Since the high-frequency substrate is more expensive than a substrate used in the intermediate frequency band, it is necessary to narrow down the area to be built by reducing the functions incorporated in the module 110. Therefore, functions that do not process high-frequency signals, such as a PLL circuit 250 that generates a voltage to be input to the VCO 120 and a power supply circuit 240 that supplies power to the module 110, are arranged in the module 210. Thereby, the power supply circuit 240 and the module 110 are connected by a connector provided between the module 110 and the module 210.

  The VCO 120 controls the output frequency by the voltage applied to the frequency control voltage terminal. The voltage Vt applied to the frequency control voltage terminal is output from the PLL circuit 250.

  Patent Document 1 discloses a configuration example of a circuit including the PLL circuit described above and a VCO.

JP 2007-158738 A

Here, the problem which generate | occur | produces is demonstrated using the microwave radio | wireless communication apparatus of FIG. The module 210 includes an intermediate frequency band amplifier 220, an intermediate frequency band amplifier 230, a PLL IC 260, a loop filter 270, and a power supply circuit 240. The PLL IC 260 has functions such as a phase comparator, a charge pump, and a frequency divider.

  The module 110 includes a VCO 120, a transmission MIX 130, a reception MIX 140, a transmission PA 150, and an LNA 160. Here, in order to suppress the power consumption of the apparatus and not to output an unnecessary signal, the power source of the transmission PA 150 is set to OFF when there is no transmission signal. Further, the GNDs of the module 110 and the module 210 are connected by screwing the respective housings. In this case, a resistance 310 is generated between the module 110 and the module 210 due to contact of the casing.

  When the resistance value of the resistor 310 is R and the current flowing through the resistor 310 is I, a potential difference calculated by V = RI is generated. Therefore, when the ground potential of the module 210 is used as a reference, the ground potential of the module 110 is not strictly equal to the ground potential of the module 210. The ground potential of the module 110 is set to GND1.

  Here, the output voltage Vt of the loop filter 270 is applied to the frequency control voltage terminal of the VCO 120. The frequency control voltage Vt is a voltage value after the voltage output from the PLL IC 260 is averaged via the loop filter 270 with respect to the phase difference detected by the phase comparator inside the PLL IC 260 of the module 210. is there. The ground potential of the module 110 is GND1. Therefore, the frequency control voltage for the VCO 120 is Vt-GND1. Thus, the VCO 120 outputs a signal having a frequency corresponding to Vt-GND1. The frequency control voltage for the VCO 120 is Vt (VCO).

  FIG. 6 shows changes in the voltages of GND1, Vt, and Vt (VCO) when the power supply of the transmission PA 150 changes from ON to OFF at time t_1. It is assumed that the current flowing through the resistor 310 when the transmission PA 150 is turned on is I = 2i, and the current flowing through the resistor 310 when the transmission PA 150 is turned off is I = i. Vt is a voltage output with respect to the phase difference of the frequency output from the VCO 120. Therefore, at time t_1, Vt does not change when the power of the transmission PA 150 of the module 110 is switched between the ON state and the OFF state.

  Further, when the power supply of the transmission PA 150 of the module 110 changes from ON to OFF, the current flowing through the resistor 310 between the module 110 and the module 210 changes. As the current flowing through the resistor 310 changes, the voltage generated at the resistor 310 also changes. Therefore, when the power of the transmission PA 150 of the module 110 changes from ON to OFF, the value of GND1 changes.

  In the example illustrated in FIG. 6, when the power supply of the transmission PA 150 is changed from ON to OFF, the current flowing through the module 110 is ½ compared to when the power supply of the transmission PA 150 is in the ON state. Therefore, the value of GND1 is also halved from 2i × R to i × R. From FIG. 6, Vt (VCO) when the power supply of the transmission PA 150 is ON is Vt (VCO) _PAON = Vt−2i × R, and Vt (time t_1) at the moment when the power supply of the transmission PA 150 is OFF VCO) is Vt (VCO) _PAOFF = Vt−i × R.

  FIG. 7 shows an example of the characteristics of the output frequency of the VCO 120 and the frequency control voltage for the VCO. When the frequency control voltage for the VCO 120 changes from Vt (VCO) _PAON to Vt (VCO) _PAOFF, the output frequency changes from F_PAON to F_PAOFF. Changes in Vt and Vt (VCO) after the output frequency fluctuates will be described again with reference to FIG. When the frequency changes, the phase difference is detected by the phase comparator inside the PLL IC 260, and the voltage output from the PLL IC 260 changes with respect to the phase difference. Vt changes according to the characteristics of the loop circuit, and the voltage of Vt (VCO) returns from Vt (VCO) _PAOFF to Vt (VCO) _PAON from time t_1 to t_2. As a result, the output frequency also returns from F_PAOFF to F_PAON. FIG. 8 shows a frequency change when the power source of the transmission PA 150 changes from ON to OFF at time t_1. The output frequency changes from F_PAON to F_PAOFF at time t_1, and then returns to F_PAON again from time t_1 to t_2. As described above, when the power state of the transmission PA 150 changes, the ground potential (GND1) of the module 110 changes. As a result, the frequency control voltage Vt (VCO) for the VCO 120 changes, and the output frequency of the VCO varies. In recent microwave radio communication apparatuses, a narrow band, multi-level modulation method is used. For this reason, when the output frequency of the VCO 120 is controlled using the PLL circuit described in FIG. 5, there arises a problem that the fluctuation of the frequency generated in accordance with the fluctuation of the ground potential leads to the deterioration of the communication quality.

  The present invention has been made to solve such problems, and it is an object of the present invention to provide a frequency control circuit and an output frequency control method that do not cause deterioration in communication quality even when the ground potential fluctuates. And

  A frequency control circuit according to a first aspect of the present invention detects a phase difference between a voltage controlled oscillator that changes an output frequency according to an input voltage, an output frequency output from the voltage controlled oscillator, and a reference frequency, A phase detector that changes the output voltage in accordance with the phase difference, and a potential difference generated by a resistance generated between a ground potential in the voltage controlled oscillator and a reference ground potential in the phase detector is added to the output voltage. And an adder for outputting to the voltage controlled oscillator.

  The output frequency control method according to the second aspect of the present invention detects the phase difference between the output frequency output from the voltage controlled oscillator that changes the output frequency according to the input voltage and the reference frequency, and determines the phase difference. A step of changing an output voltage to be output in response, a step of adding the output voltage, and a potential difference between a ground potential in the voltage controlled oscillator and a reference ground potential connected to the ground potential via a resistor; And outputting the added voltage to the voltage controlled oscillator.

  According to the present invention, it is possible to provide a frequency control circuit and an output frequency control method that do not deteriorate communication quality even when the ground potential varies.

1 is a configuration diagram of a wireless communication apparatus according to a first exemplary embodiment. 1 is a configuration diagram of a wireless communication apparatus according to a first exemplary embodiment. It is a figure which shows the change of the voltage when the power supply state of the amplifier concerning Embodiment 1 is changed. It is a block diagram of the radio | wireless communication apparatus using a general PLL circuit. It is a block diagram of the radio | wireless communication apparatus using a general PLL circuit. In a wireless communication apparatus using a general PLL circuit, it is a diagram showing a change in voltage when the power supply state of the amplifier is changed. It is a figure which shows the relationship between the control voltage and output frequency in a common voltage controlled oscillator. In a wireless communication device using a general PLL circuit, it is a diagram showing a change in output frequency when the power supply state of the amplifier is changed.

(Embodiment 1)
Embodiments of the present invention will be described below with reference to the drawings. A configuration example of the wireless communication apparatus according to the first exemplary embodiment of the present invention will be described with reference to FIG. The wireless communication apparatus includes a voltage controlled oscillator 10, a phase detector 11, and an adder 12.

  The voltage controlled oscillator 10 changes the output frequency according to the input voltage. The voltage controlled oscillator 10 is referred to as a VCO (Voltage Controlled Oscillator), and is an oscillator that uses a changing output frequency as an oscillation frequency.

  The phase detector 11 is a phase difference between a reference frequency input by dividing a frequency output from a crystal oscillator or the like (not shown) or a crystal oscillator or the like and an output frequency output from the voltage controlled oscillator 10. And the output voltage Vt to be output is changed according to the phase difference. For example, the phase detector 11 compares the reference frequency and the output frequency, and changes the output voltage Vt in order to control the output frequency and the reference frequency so as to match. As described in FIG. 7, assuming that the output frequency increases as the voltage input to the voltage controlled oscillator 10 increases, the phase detector 11 outputs an output signal when the output frequency is lower than the reference frequency. The voltage Vt to be controlled is increased so that the frequency output from the voltage controlled oscillator 10 is increased.

  A potential difference between the ground potential in the voltage controlled oscillator 10 and the reference ground potential 13 in the phase detector 11 is defined as GND1. The adder 12 adds the output voltage Vt output from the phase detector 11 and GND1, and outputs the result to the voltage controlled oscillator 10. Here, the relationship between the reference ground potential 13 in the phase detector 11 and the ground potential in the voltage controlled oscillator 10 will be described. For example, when the voltage controlled oscillator 10 is grounded by being screwed to a housing including the voltage controlled oscillator 10, and the reference ground potential 13 is also grounded by being screwed to the housing having the phase detector 11. In addition, the ground potential is connected by connecting the respective casings. In this case, by connecting the housing, a resistor 14 is generated between the reference ground potential 13 in the phase detector 11 and the ground potential in the voltage controlled oscillator. When the resistance value of the resistor 14 is R and the current flowing through the resistor 14 is I, the ground potential in the voltage controlled oscillator 10 is I × R higher than the reference ground potential 13 when the reference ground potential 13 is used as a reference.

  The adder 12 adds the output voltage Vt output from the phase detector 11 and the potential difference GND1, and outputs Vt (VCO) = Vt + GND1 to the voltage controlled oscillator 10.

  Here, when a switch of an amplifier or the like (not shown) in the wireless communication apparatus is switched ON or OFF, the value of the current flowing in the wireless communication apparatus changes. For example, a case where an amplifier is connected to the voltage controlled oscillator 10 and there is no transmission signal to be transmitted from the wireless communication apparatus to the external apparatus will be described. Thus, by turning off the switch of the amplifier, it is possible to suppress the output of unnecessary signals.

  When the amplifier switch is ON, the current flowing to the reference ground potential 13 is 2i, and when the amplifier switch is OFF, the current flowing to the reference ground potential 13 is i. In this case, the voltage generated in the resistor 14 is 2i × R when the amplifier switch is in the ON state, and i × R when the amplifier switch is in the OFF state. Thereby, the ground potential in the voltage controlled oscillator 10 is changed by switching the switch of the amplifier to ON or OFF.

  Here, the voltage V (VCO) in the voltage controlled oscillator 10 is Vt (VCO) −GND1 obtained by subtracting the ground potential GND1 in the voltage controlled oscillator 10 from the voltage Vt (VCO) input from the adder 12. Since Vt (VCO) = Vt + GND1, V (VCO) = Vt. Thus, the voltage V (VCO) in the voltage controlled oscillator 10 is determined by Vt output from the phase detector 11 regardless of the value of GND1.

  As described above, by providing the adder 12 in the wireless communication apparatus in FIG. 1, the voltage Vt (VCO) obtained by adding the voltage Vt output from the phase detector 11 and the ground potential GND1 in the voltage controlled oscillator 10 is added. ) Can be output. As a result, in the voltage controlled oscillator 10, it is possible to prevent deterioration in communication quality by suppressing fluctuations in the output frequency due to fluctuations in the ground potential.

  Subsequently, a detailed configuration example of the wireless communication apparatus according to the first exemplary embodiment of the present invention will be described with reference to FIG. The wireless communication apparatus includes a high frequency band module 21 that performs processing of a high frequency signal and an intermediate frequency band module 22. The high frequency band module 21 includes a voltage controlled oscillator 10, a mixer 23, a mixer 24, a power amplifier (PA) 25, and a low noise amplifier (LNA) 26. The intermediate frequency band module 22 includes a phase detector 11, an adder 12, a power source 36, an amplifier 37, and an amplifier 38. The phase detector 11 has a PLL IC 27 and a loop filter 28. The adder 12 includes resistors 29 to 33, an operational amplifier 34, and an operational amplifier 35.

  The voltage controlled oscillator 10, the mixer 23, the mixer 24, the power amplifier (PA) 25, and the low noise amplifier (LNA) 26 are accommodated in the casing for the high frequency band module 21. Here, the casing for the high frequency band module 21 is made of metal, and includes a voltage controlled oscillator 10, a mixer 23, a mixer 24, a power amplifier (PA) 25, and a low noise amplifier (LNA) 26. Shield. Further, the potential of the housing for the high frequency band module 21 is set to GND1. The phase detector 11, the adder 12, the power source 36, the amplifier 37, and the amplifier 38 are accommodated in a housing for the intermediate frequency band module 22. Here, the casing for the intermediate frequency band module 22 is made of metal, and shields the phase detector 11, the adder 12, the power source 36, the amplifier 37, and the amplifier 38. Further, the potential of the housing is set to the reference ground potential 13.

  The housing for the high frequency band module 21 and the housing for the intermediate frequency band module 22 are connected, for example, by screwing each housing. Alternatively, each housing may be connected by a connector. Therefore, a resistor 14 is generated between the housings. That is, the connection resistance of the housing is the resistance 14.

  The voltage controlled oscillator 10 outputs a frequency signal that changes in accordance with a change in the input voltage input from the adder 12 to the mixer 23 and the mixer 24. The mixer 23 converts the intermediate frequency signal input from the amplifier 37 of the intermediate frequency band module 22 into a high frequency signal using the frequency signal input from the voltage controlled oscillator 10. The PA 25 amplifies the power of the high frequency signal generated by the mixer 23 and outputs it to an external device. The PA 25 is set to the OFF state when there is no signal to be output to the external device, and is set to the ON state when there is a signal to be output to the external device. A high frequency signal is input to the LNA 26 from an external device. The mixer 24 converts the high frequency signal output from the LNA 26 into an intermediate frequency signal. The mixer 24 outputs the intermediate frequency signal to the amplifier 38 of the intermediate frequency band module 22.

  The PLL IC 27 acquires the output frequency signal output from the voltage controlled oscillator 10. The PLL IC 27 compares the phase of the acquired output frequency signal with the phase of the reference frequency signal. The PLL IC 27 outputs an output voltage corresponding to the comparison result. That is, the PLL IC 27 controls the output voltage so that the phase of the output frequency signal is the same as the phase of the reference frequency signal. Alternatively, the PLL IC 27 controls the output voltage so that the output frequency and the reference frequency are the same. Thus, the PLL IC 27 includes a circuit having a function of a phase comparator that compares the phase of the output frequency signal and the phase of the reference frequency signal, and a function of a charge pump or the like that changes the output voltage. Further, the PLL IC 27 may include a circuit having a function of a frequency divider that divides the output frequency signal output from the voltage controlled oscillator 10. In this case, the phase comparator compares the phase of the divided frequency signal with the phase of the reference frequency signal, or compares the divided frequency with the reference frequency. Thus, it has a function as a frequency divider, and the frequency of the frequency signal output from the voltage controlled oscillator 10 can be changed by changing the frequency dividing ratio of the frequency divider. The PLL IC 27 outputs a voltage to the loop filter 28. The loop filter 28 rectifies the output voltage and outputs it to the adder 12.

  Next, a configuration example of the circuit in the adder 12 will be described. The resistor 29 and the resistor 30 are connected in parallel, and a node between the resistor 29 and the resistor 30 is connected to the resistor 31. Further, the resistor 31, the resistor 32, and the resistor 33 are connected in series. Further, the resistors 29 to 33 all have the same resistance value Ra. Here, the negative terminal of the operational amplifier 34 is connected to the nodes of the resistors 29, 30 and 31. The positive terminal of the operational amplifier 34 is grounded to GND. The output terminal of the operational amplifier 34 is connected to the nodes of the resistors 31 and 32. The negative terminal of the operational amplifier 35 is connected to the nodes of the resistors 32 and 33. The positive terminal of the operational amplifier 35 is grounded to GND. The output terminal of the operational amplifier 35 is connected to the resistor 33 and the voltage controlled oscillator 10.

  The voltage Vt output from the loop filter 28 is input to the resistor 30 of the adder 12. The casing of the high frequency band module 21 is connected to one end of the resistor 29 of the adder 12. That is, the potential at one end of the resistor 29 is GND1. The negative terminal of the operational amplifier 34 has the same potential as the positive terminal GND due to a virtual short circuit. Therefore, the current flowing through the resistor 29 is GND1 / Ra. Similarly, the current flowing through the resistor 30 is Vt / Ra. Since the input impedance of the operational amplifier 34 is sufficiently large, all the currents flowing through the resistors 29 and 30 are considered to flow through the resistor 31. Therefore, the output OP34_out of the operational amplifier 34 is OP34_out = −Ra × {(GND1 / Ra) + (Vt / Ra)} = − (GND1 + Vt). Furthermore, since the negative terminal of the operational amplifier 35 also has the same potential as the positive terminal GND due to a virtual short circuit, the current flowing through the resistor 32 is − (GND1 + Vt) / Ra. Since the input impedance of the operational amplifier 35 is sufficiently large, all the current flowing through the resistor 32 is considered to flow through the resistor 33. Therefore, the output OP35_out of the operational amplifier 35 is OP35_out = −Ra × {− (GND1 + Vt) / Ra} = GND1 + Vt. That is, the adder 12 outputs the result of adding the output Vt of the loop filter 28 and GND1 of the high frequency band module 21.

  Here, OP35_out is a voltage applied to the voltage terminal of the voltage controlled oscillator 10. The ground potential of the high frequency band module 21 is GND1. Therefore, the frequency control voltage Vt (VCO) in the voltage controlled oscillator 10 is Vt (VCO) = OP35_out−GND1. Since OP35_out = GND1 + Vt, Vt (VCO) = Vt. As a result, even if the power of the PA 25 or the LNA 26 is switched from ON to OFF or from OFF to ON, the frequency control voltage Vt (VCO) is maintained even if the current in the wireless communication device, that is, the value of the current flowing through the resistor 14 changes. Operates to remain constant. A state of changes in GND1, OP35_out, and Vt (VCO) when the power supply of the PA 25 is switched from ON to OFF will be described with reference to FIG.

  PA25 is switched from ON to OFF at time t_1. When PA25 is in the ON state, the current flowing through the reference ground potential 13 is 2i. When PA25 is in the OFF state, the current flowing through the reference ground potential 13 is i. Therefore, GND1 is increased by 2i × R with respect to the reference ground potential 13 of the intermediate frequency band module 22 when PA25 is in the ON state, and is increased by i × R when PA25 is in the OFF state. In OP35_out, the output voltage decreases when PA25 is in the OFF state by the amount GND1 decreases at t_1. The output voltage Vt output from the loop filter 28 and the frequency control voltage Vt (VCO) have the same value because of the relationship Vt (VCO) = Vt. Further, Vt is a voltage output with respect to the phase difference between the output frequency output from the voltage controlled oscillator 10 and the reference frequency, and therefore does not change by switching the PA 25 between the ON state and the OFF state. Therefore, the values of Vt and Vt (VCO) do not change at the time t_1, and are kept constant.

  As described above, in the apparatus in which the voltage controlled oscillator 10 and the phase detector 11 and the adder 12 are configured as different modules, the potential difference of the ground potential between the high frequency band module 21 and the intermediate frequency band module 22 varies. In this case, by controlling the frequency of the voltage controlled oscillator 10 using the voltage obtained by adding the ground potential GND1 of the high frequency band module 21 and the output voltage Vt, it is possible to suppress the frequency fluctuation due to the potential difference of the ground potential. .

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 Voltage control oscillator 11 Phase detector 12 Adder 13 Reference ground potential 14 Resistance 21 High frequency band module 22 Intermediate frequency band module 23, 24 Mixer 25 PA
26 LNA
27 PLL IC
28 Loop filter 29-33 Resistor 34, 35 Operational amplifier 36 Power supply 37, 38 Amplifier

Claims (5)

A voltage controlled oscillator that changes the output frequency according to the input voltage; and
A phase detector for detecting a phase difference between an output frequency output from the voltage controlled oscillator and a reference frequency, and changing an output voltage according to the phase difference;
An adder that adds a potential difference generated by a resistance generated between a ground potential in the voltage-controlled oscillator and a reference ground potential in the phase detector to the output voltage and outputs the difference to the voltage-controlled oscillator. circuit. The adder is
The operational amplifier which inputs the potential difference produced by the resistance which generate | occur | produces between the ground potential in the said voltage control oscillator and the reference | standard ground potential in the said phase detector, and the said output voltage to one input terminal. Frequency control circuit.   The frequency control according to claim 1, further comprising a mixer that generates a high-frequency signal by multiplying an input signal using a frequency in an intermediate frequency band by an output frequency output from the voltage-controlled oscillator. circuit.   The ground potential in the voltage controlled oscillator is a ground potential in a module different from the phase detector, and the resistor connects the ground potential in the voltage controlled oscillator and the reference ground potential in the phase detector. The frequency control circuit according to claim 1, wherein the frequency control circuit is generated. Detecting the phase difference between the output frequency output from the voltage controlled oscillator that changes the output frequency according to the input voltage and the reference frequency, and changing the output voltage to be output according to the phase difference;
Adding the output voltage and a potential difference between a ground potential in the voltage controlled oscillator and a reference ground potential connected to the ground potential via a resistor;
Outputting the added voltage to the voltage controlled oscillator.

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