JP3205248B2 - Frequency adjustment device for voltage controlled oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency control device for a voltage controlled oscillation circuit for adjusting an oscillation frequency of a voltage controlled oscillation circuit (VCO) to a target frequency.

[0002]

2. Description of the Related Art It is necessary to adjust the frequency of a VCO because the frequency of the VCO varies due to variations in ICs. As a conventional means for adjusting the oscillation frequency of a VCO, means for changing the value of external components of the IC has been used. Hereinafter, a description will be given of the conventional frequency adjusting device of the voltage controlled oscillation circuit. FIG. 4 is a diagram of a frequency adjusting device of a conventional voltage controlled oscillator circuit, wherein 1 is a power supply terminal, 2 and 3 are built-in resistors, 4 is a differential amplifier, 5 is an NPN transistor, 6 is an adjusting terminal, and 7 is a frequency adjusting device. A variable resistor, 8 is a VCO, and 9 is an output terminal.

An arbitrary potential V is set by built-in resistors 2 and 3 connected in series between a power supply terminal 1 and a ground (referred to as GND).
A midpoint with ₁ is constructed. The output of the differential amplifier 4 having this midpoint as a positive input is input to the base of the NPN transistor 5, and the emitter of the NPN transistor 5 is connected to the adjustment terminal 6
And the negative input of the differential amplifier 4. Adjustment terminal 6 and G
A frequency adjusting variable resistor 7 is connected between ND. Also, N
The collector of the PN transistor 5 is input to the VCO 8,
An electrical waveform having an oscillation frequency determined by the current is output from the output terminal 9.

[0004] The voltage controlled oscillation circuit configured as described above.
The operation of the frequency adjustment device is described below.
You. The resistance between the power supply voltage Vcc of the power supply terminal 1 and the built-in resistors 2 and 3
Resistance value R _Two, R_ThreeThe positive input voltage V of the differential amplifier 4₊But
decide. This positive input voltage V₊Is V₊= ｛R_Three/ (R_Two+ R_Three)｝ × Vcc.

The negative input of the differential amplifier 4 has the same potential as the positive input (virtual ground of the differential amplifier) and has a low impedance. The output of the differential amplifier 4 becomes higher than the positive input voltage by V _BE (base-emitter voltage of the NPN transistor 5). Next, the potential V ₀ of the adjustment terminal 6 is
Since the input is the same as the negative input of the differential amplifier 4, the emitter current I of the NPN transistor 5 is increased or decreased by changing the variable resistor 7 for frequency adjustment. NPN transistor 5
Is the resistance value R of the frequency adjusting variable resistor 7.
When _{B, I = V + / R} B = (1 / R B) × {R 3 / (R 2 +
R ₃ )｝ × Vcc.

[0006] Since the NPN transistor 5 is usually in the non-saturation region, the emitter current is equal to the collector current.
Input to O8. Generally VCO oscillation frequency f capacitance of the internal input current I and the VCO 8 C, determined by the internal voltage V _B. As a result, the frequency f output to the output terminal 9
Is f = I / CV _B = (1 / R _B ) × ｛R ₃ / (R ₂ + R ₃ )｝ × Vcc × 1 / CV
Given in _B.

[0007]

However, in the above conventional configuration, it is necessary to adjust the frequency adjusting variable resistor 7 in order to adjust the output frequency to a target value. Therefore, there is a problem that the number of adjustment steps for the IC user increases, and the cost increases. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a frequency control device for a voltage-controlled oscillation circuit which can eliminate an adjustment process for an IC user.

[0008]

According to a first aspect of the present invention, there is provided a frequency control apparatus for a voltage-controlled oscillation circuit, the oscillation frequency of which is changed by a current.
A conversion circuit for converting serial data input from the outside into parallel data, and a PRO for holding the parallel data
M, a digital / analog conversion circuit for converting the digital information of the PROM into an analog quantity, a low impedance reference voltage generation circuit connected to the output of the digital / analog conversion circuit, and an output of the digital / analog conversion circuit. A differential amplifier connected to the input, the negative input connected to the output terminal, and a fixed resistor connected between the output terminal and the ground. This flows through the control oscillation circuit.

According to the frequency adjusting apparatus of the voltage controlled oscillation circuit according to the first aspect, the digital-analog conversion circuit is controlled by the serial control of the conversion circuit, and the predetermined current is supplied to the voltage controlled oscillation circuit. Since the oscillation frequency of the control oscillation circuit is limited to a desired frequency and serial control data can be written in the PROM, variations in the VCO frequency due to variations in the IC can be adjusted by, for example, serial data when the IC is shipped. For this reason, the adjustment process for the IC user can be eliminated, the number of pins can be reduced and the number of components can be reduced, and the assembly cost for the IC user can be reduced.

According to a second aspect of the present invention, there is provided a frequency control apparatus for a voltage controlled oscillation circuit according to the first aspect, wherein an internal resistor of an IC is used as a fixed resistor, and an output of a temperature compensation circuit of the internal resistor is connected to a positive input of a differential amplifier. Connected. According to the frequency control apparatus of the voltage controlled oscillator according to the second aspect, in addition to the effects of the first aspect, even if an internal resistor is used as the resistor for determining the current of the voltage controlled oscillator, the influence of the temperature is avoided by the temperature compensation circuit. be able to.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram of a frequency adjustment device of a voltage controlled oscillation circuit according to the first embodiment. FIG.
In the figure, reference numerals 10 and 11 denote serial data input terminals for adjusting the VCO oscillation frequency.
2, converts the input serial data into parallel data, outputs the parallel data to a PROM (programmable read only memory) 13, and outputs the output to a digital / analog conversion circuit (DAC) 1
4, the output of the DAC 14 is connected to the positive input of the differential amplifier 4 and one end of a built-in resistor 15 for voltage conversion. 1
Reference numeral 8 denotes a write terminal of the PROM 13. Also, the output of a buffer amplifier 16 having an input at the midpoint of the internal resistors 2 and 3 connected in series between the power supply terminal 1 and GND is connected to the other end of the internal resistor 15 for voltage conversion to provide a low impedance reference voltage. Is generated.

Reference numeral 4 denotes a differential amplifier, reference numeral 5 denotes an NPN transistor, and reference numeral 6 denotes an adjustment terminal which has the same configuration as that of the conventional example. An external fixed resistor 17 is connected between the adjustment terminal 6 and GND. Reference numeral 8 denotes a VCO, and reference numeral 9 denotes its output terminal, which are also the same as those in the conventional example. The operation of the VCO oscillation frequency adjusting device thus configured will be described below. First, the oscillation frequency of the VCO 8 at the output terminal 9 is measured. VC so that the frequency matches the target frequency
O oscillation frequency adjustment serial data input terminals 10 and 11
Of the VCO oscillation frequency adjustment serial data.
The optimum serial data when the oscillation frequency of the output terminal 9 approaches the target frequency is found, and the optimum data is input to the PROM 13 as adjustment data via the serial / parallel conversion circuit 12. When the PROM 13 receives the optimum adjustment data, it applies a write pulse to the PROM write terminal 18 to change the stored optimum adjustment data to PROM.
It is fixed in the ROM 13. PROM1 written once
The adjustment data of No. 3 is unchanged and is output to the DAC 14. Therefore, since the DAC 14 always outputs the constant current i _D , the positive input voltage V ₊ of the differential amplifier 4
And the midpoint potential V ₁ = VccR ₃ / (R ₂
+ R ₃ ), it is represented by V ₊ = i _D × R + V ₁ .
The positive and negative inputs of the differential amplifier 4 becomes the same potential, and the negative input is connected to the adjustment output terminal 6, the voltage V ₀ which adjustment output terminal 6 is the same as V _+. Since the fixed resistor 17 is connected between the output terminal 6 for adjustment and GND, the emitter current I of the NPN transistor 5 is represented by the following equation: If the resistance value of the fixed resistor 17 is R _Z , I = V ₀ / R _Z = (i _D × R + V ₁ ) / R _Z. Therefore, the frequency f of the prior art as well as the output terminal 9, an internal capacitance C of the VCO 8, when the internal voltage V _B of _{VCO8, f = I / CV B} = {(i D R + V 1) / R Z ｝ × (1 / CV _B ) (1)

Next, the temperature characteristic of the equation (1) will be described. Power supply terminal 1 voltage Vcc and built-in resistor 2
(R ₂ ), 3 (R ₃ ) are connected in series, and the voltage V ₁ at the midpoint determined, the internal capacitance C of the VCO 8 and the internal voltage V _B ,
The fixed resistance 17 (R _Z ) generally does not depend on temperature. Further, the temperature characteristic of the output current i _D of the _DAC 14 is
(R), the output frequency f _T becomes
5 When the temperature coefficient .alpha.T of _{(R), f T = [} {(i D / αT) × (R × αT) + V 1} / R Z] × 1 / CV B = {(i D × R + V ₁ ) / R _Z / × 1 / CV _B = f It can be seen that it is independent of temperature.

Next, the power supply voltage fluctuation characteristic of the equation (1) will be described. In the equation (1), the fixed resistance 17 (R _Z )
And the internal capacitance C of the VCO 8 is independent of the fluctuation of the power supply voltage. On the other hand, the voltage V ₁ of the midpoint of the internal voltage V _B and the voltage Vcc and the internal resistor 2 and 3 of the power source terminal 1 as determined by series connection of VCO8 varies at the same rate with respect to supply voltage variation. Also, the output current i _{D of the} DAC 14 is changed at the same rate with respect to the power supply voltage fluctuation. The output frequency f _V when the power supply voltage changes by ΔV is

[0015]

(Equation 1)

Thus, it can be seen that there is no relation to the power supply voltage fluctuation. According to the first embodiment, the DAC 14 is controlled by the serial control of the conversion circuit 12 to supply a predetermined current to the VCO 8 so that the oscillation frequency of the VCO 8 is limited to a desired frequency. Since data can be written to the PROM 13, variations in VCO frequency due to variations in IC
For example, it can be adjusted by serial data when the IC is shipped. For this reason, the adjustment process for the IC user can be eliminated, the number of pins can be reduced and the number of components can be reduced, and the assembly cost for the IC user can be reduced.

Further, the VCO frequency can be adjusted with high accuracy, and a stable VCO frequency can be maintained even with respect to temperature characteristics and power supply voltage fluctuation. 2 and 3 show a second embodiment of the present invention. FIG. 2 is a configuration diagram of a frequency adjustment device of a voltage controlled oscillation circuit according to a second embodiment. In FIG. 2, 10 and 11 are serial data input terminals for VCO frequency adjustment, 12 is a serial / parallel conversion circuit, and 13 is P
ROMs, which are the same as those in the configuration of the first embodiment. The output of the DAC 14 is connected to the positive input of the differential amplifier 4, the internal resistor 15 for voltage conversion, and the temperature compensation circuit 19. 1 is a power supply terminal, 2 and 3 are built-in resistors, 16 is a buffer amplifier, 4 is a differential amplifier, 5 is an NPN transistor, 1
Reference numeral 8 denotes a PROM writing terminal, which has the same configuration as that of the first embodiment.

A built-in resistor 20 for current conversion is connected to the negative input of the differential amplifier 4, and the other end is connected to GND. Reference numeral 8 denotes a VCO, and 9 denotes an output terminal. These are the same as those of the conventional example. The operation of the frequency control device of the voltage controlled oscillation circuit thus configured will be described below. While measuring the oscillation frequency of the output terminal 9, the input terminals 10, 11
By inputting more serial data and driving the DAC 14, the oscillation frequency of the VCO 8 is changed. When the oscillation frequency of the VCO 8 reaches a desired value, a write pulse is applied from the PROM write terminal 18 to cause the PROM 13 to hold optimal data, and the oscillation frequency of the output terminal 9 is fixed.

In this case, regarding the power supply voltage fluctuation, the first
There is no dependency as in the embodiment of FIG. The temperature characteristics are
In the first embodiment, the frequency adjusting resistor that determines the current flowing through the VCO 8 is the fixed resistor 17 and has no dependency because it is outside the IC. However, in this embodiment, the resistor is the built-in resistor 20 of the IC. The VCO
Frequency depends on temperature. Therefore, the temperature dependence of the internal resistance is canceled by using the temperature compensation circuit 19, so that the VCO frequency does not depend on the temperature.

An example of the temperature compensation circuit 19 will be described below with reference to FIG. The output of the constant current source 21 is connected to the anode of the diode D ₁ and the positive input of the differential amplifier 24, and the negative input and output of the differential amplifier 24 are connected to the emitter of the transistor 23. The base was connected to the output to diode D ₂ of Atodo the transistor 23 of the current source 22 which outputs a current I ₂ is proportional to the temperature, to connect the cathode of the diode D ₂ to the anode of the diode D _3, thereby the temperature A compensation circuit 19 is configured. The current I ₂ proportional to the temperature is calculated as V _T (kT /
This can be realized by creating a current source proportional to q). At this time, the currents I ₁ and I ₂ are set so as to have a relationship of I ₂ = I ₁ (Ta−To) where the ambient temperature is Ta and the temperature To is such that I ₂ = 0. Assuming that V _T = kT / q and saturation current Is, the base potential V _B and the emitter potential V _E of the transistor 23 are V _B = 2V _T × lnｌI ₁ (Ta−To) / Is｝ V _E = V _T × ln (I ₁ / Is). Therefore, the output current Io is

[0021]

(Equation 2)

[0022] expressed as, consequently the output current Io is proportional to the square of the temperature to the constant current I _1. Since the diffusion resistance inside the IC, that is, the built-in resistance 20, has a quadratic coefficient with respect to the temperature, the characteristic changes with a quadratic curve. In response to this characteristic, a current proportional to the square of temperature causes
By canceling the following characteristics, the current independent of temperature
Can be made internally. As a result, even if the built-in resistor 20 for the VCO frequency adjustment resistor is built in, the temperature independent V
CO frequency can be obtained.

As described above, according to this embodiment, the VCO frequency adjustment caused by individual IC variations is
It can be realized by adjusting the serial data at the time of shipment of the IC and writing individual optimum data to the PROM. In addition, it is possible to maintain a highly accurate VCO frequency that is stable with respect to temperature characteristics and power supply voltage fluctuation.

[0024]

According to the frequency control apparatus of the voltage controlled oscillation circuit according to the first aspect, the digital-analog conversion circuit is controlled by the serial control of the conversion circuit to supply a predetermined current to the voltage controlled oscillation circuit. Thus, the oscillation frequency of the voltage controlled oscillation circuit is limited to a desired frequency, and the serial control data can be written into the PROM. Therefore, the variation in the VCO frequency due to the variation in the IC can be adjusted by, for example, serial data at the time of shipment of the IC. For this reason, the adjustment process for the IC user can be eliminated, the number of pins can be reduced and the number of components can be reduced, and the assembly cost for the IC user can be reduced.

According to the frequency adjusting device of the voltage controlled oscillator according to the second aspect, in addition to the effect of the first aspect, even if an internal resistor is used as the resistor for determining the current of the voltage controlled oscillator, the influence of the temperature by the temperature compensating circuit can be obtained. Can be avoided.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment.

FIG. 3 is a temperature compensation circuit diagram.

FIG. 4 is a circuit diagram of a conventional example.

[Explanation of symbols]

 4 Differential Amplifier 8 Voltage Controlled Oscillator (VCO) 12 Serial / Parallel Converter 13 PROM 14 Digital / Analog Converter (DAC) 15 Resistor 17 Fixed Resistor 19 Compensation Circuit 20 Built-in Resistance 25 Low Impedance Reference Voltage Generation Circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03L 7/00 H03B 5/32 H03L 1/02

Claims (2)

(57) [Claims] 1. A frequency adjustment device for a voltage-controlled oscillation circuit whose oscillation frequency is changed by a current, comprising: a conversion circuit for converting serial data input from the outside into parallel data; a PROM holding the parallel data; A digital / analog conversion circuit for converting the digital information of the PROM into an analog quantity; a low impedance reference voltage generating circuit connected to the output of the digital / analog conversion circuit; and an output of the digital / analog conversion circuit as a positive input A differential amplifier having a fixed resistor connected between the output terminal and the ground, the negative input being connected to the output terminal,
A frequency control device for a voltage controlled oscillation circuit, wherein a current determined by the voltage of the output terminal of the differential amplifier and the magnitude of the fixed resistor flows through the voltage controlled oscillation circuit. 2. An internal resistor of an IC is used as a fixed resistor.
2. The frequency adjusting device according to claim 1, wherein an output of the temperature compensation circuit having the built-in resistor is connected to a positive input of the differential amplifier.