KR20010011261A - Radio Frequency Modulator Expanding Variable Range of Oscillating Frequency of RF signal - Google Patents

Abstract

PURPOSE: A radio frequency converter for widening an oscillating frequency variable range of a radio frequency signal is provided to realize a coil using a gyrator such that an inductance value is varied in a radio frequency oscillator, thereby increasing the oscillating frequency variable range. CONSTITUTION: A radio frequency converter includes a phase comparator for phase-comparing a reference oscillation signal with a radio frequency oscillation signal and a charge pump(470) for increasing or decreasing current in response to the result of the phase comparator and outputting the increased or decreased result. The radio frequency converter further includes a loop filter(480) for low-pass-filtering the output signal of the charge pump and outputting the filtered result as a control voltage, a mutual conductance controller(430) for controlling a mutual conductance in response to an external switching control signal and outputting the controlled result as a mutual conductance control signal, and a radio frequency oscillator for varying an inductance value in response to the mutual conductance control signal, changing a capacitance value based on the control voltage and varying the frequency of the radio frequency oscillation signal according to the changed inductance and capacitance values.

Description

Radio Frequency Modulator Expanding Variable Range of Oscillating Frequency of RF Signal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio frequency modulator (RF modulator) using a phase locked loop (PLL), and more particularly, to a radio frequency modulator for widening an oscillation frequency variable range of a high frequency signal.

In general, RF modulators, or RF modulators, are primarily used in video cassette recorders (VCRs), video tape recorders (VTRs), satellite video receivers (SVRs), and game machines. The apparatus for converting a video signal and an audio signal reproduced by the recording and reproducing apparatus into a specific RF channel frequency and outputting the same.

In addition, the RF modulator may be divided into ultra high frequency (VHF) and ultra high frequency (UHF) according to a frequency using band. That is, the VHF method mainly uses two specific channels, and the UHF method uses 12 or more channels. In particular, a conventional RF modulator using a VHF phase locked loop (PLL) uses an oscillation signal of 15.625 KHz as a reference divided signal for phase detection in a PLL for an audio signal and a PLL for an image signal.

1 is a block diagram illustrating a conventional RF modulator, a programmable counter 100, a prescaler 120, a high frequency (RF) oscillator 140, a reference oscillator 110, a reference divider 130, and a phase. Detector 160, charge pump 180 and loop filter 190.

The RF modulation device shown in FIG. 1 shows an example of a modulation device for four channels used in the United States, and the RF oscillation signal RF_OSC may be set to 67.25 MHz. Here, the reference oscillator 110 generally uses a reference oscillation signal REF_OSC of 4 MHz, and the reference divider 130 divides the reference oscillation signal REF_OSC of 4 MHz by 256 to generate an oscillation signal having a frequency of 15.625 KHz. Create (REF_D). That is, the divided reference signal REF_D is compared in phase with the divided RF signal RF_D output from the programmable counter 100 in the phase detector 160. The charge pump 180 increases or decreases the current according to the phase comparison result detected by the phase detector 160, and the loop filter 190 filters the low pass components in the output signal of the charge pump 180 and controls correspondingly thereto. Generate the voltage Vt. At this time, the RF oscillator 140 controls the frequency of the initial RF oscillation signal RF to be 15.625 KHz * N corresponding to the control voltage Vt. Accordingly, the output of the RF oscillator 140 is output as the RF oscillation signal RF_OSC, and the prescaler 120 divides the RF oscillation signal RF_OSC into eight and applies it to the programmable counter 100. The programmable counter 100 determines a division ratio for dividing an output signal of the prescaler 120 by changing a counter value in response to a microprocessor or an externally applied switching control signal CON.

The most important problem in the RF modulation device as described above may be said to be implemented to be applicable to multiple channels and multiple countries. Therefore, it is very important that the RF modulator implement an RF oscillator capable of covering the frequency of the unique carrier signal assigned to each country or each channel.

FIG. 2 is a detailed circuit diagram illustrating the high frequency oscillator 140 of the RF modulator shown in FIG. 1 and includes a first oscillator 20 and a second oscillator 25. Here, the first oscillator 20 is a part implemented outside the chip, and includes a capacitor C20, a baricap diode VD20, and a coil L20. In addition, the second oscillator 25 is a part embedded in the chip, and is implemented as the oscillation element 27.

The high frequency oscillation signal RF_OSC output from the high frequency oscillator 140 shown in FIG. 2 is determined by the inductance of the coil L20 and the capacitance value of the VARICAP DIODE VARI50. The oscillation frequency of the high frequency oscillation signal RF_OSC is represented as follows.

Here, C _VD20 represents the capacitance of the barrier cap diode VD20. That is, the control voltage Vt output from the loop filter 190 of FIG. 1 is applied as a reverse voltage of the barrier cap diode VD20 of the high frequency oscillator 140. In general, Vt uses a voltage in the range of 0 to 5V. do.

3 is a diagram showing capacitance characteristics of a general barrier cap diode VD20. Referring to FIG. 3, it can be seen that as the reverse voltage in the range of 0 to 5V increases, the capacitance decreases. For example, when the reverse voltage is 0V, the capacitance of the varicap diode VD20 has a value of C1, and when 5V, the capacitance of the varicap diode VD20 has a value of C2.

That is, as shown in FIG. 3, the variable range of the high frequency oscillation signal is determined only by the rate of change of the capacitance value of the barrier cap diode VD20, that is, C_RATIO (= C2 / C1) at a power supply voltage of 5V. In practice, the frequency of the RF signal Will change in proportion to

However, the frequency band of the carrier signal of the RF modulator shown in FIG. 1 is distributed over a wide frequency band of approximately 40 MHz to 250 MHz. However, at present, a method for covering the entire frequency band without changing external application circuits has not been proposed yet. In other words, for a multi-country or multi-channel, the frequency variable range needs to be wide, so that a barrier cap diode with a large change in capacitance is used as much as possible. However, a typical baricap diode has a capacitance change rate of about 3 to 4, and the capacitance change rate of this degree is difficult to apply to a desired country or channel. In order to solve this problem, conventionally, a method of manufacturing by changing the value of the coil provided outside the chip in each country or each channel in the RF oscillator is used, but there is a limit to fully cope with different countries and channels have. In addition, as shown in FIG. 2, when the coil is an external type provided outside the chip, there is a possibility that a problem of variation in inductance may occur during production or due to external factors.

An object of the present invention is to provide a radio frequency modulation apparatus that can widen the oscillation frequency variable range of a high frequency signal by implementing a coil using a gyrator to change the inductance value in the high frequency oscillator.

1 is a block diagram illustrating a conventional radio frequency modulation apparatus using a phase locked loop.

FIG. 2 is a circuit diagram illustrating a high frequency oscillator of the radio frequency modulation device shown in FIG. 1.

3 is a view for explaining the capacitance characteristics of a typical baricap diode.

Figure 4 is a block diagram of an embodiment for explaining the radio frequency modulation apparatus widening the oscillation frequency variable range of the high frequency signal according to the present invention.

FIG. 5 is a detailed circuit diagram illustrating a high frequency oscillator of the radio frequency modulation device shown in FIG. 4.

FIG. 6 is a detailed circuit diagram illustrating the variable coil of the high frequency oscillator shown in FIG. 5.

FIG. 7 is a circuit diagram illustrating the mutual conductance adjusting unit of the radio frequency modulation device shown in FIG. 4.

In order to achieve the above object, a radio frequency modulation device in which the oscillation frequency variable range of a high frequency signal according to the present invention is widened, a phase comparison between an N (> 1) divided reference oscillation signal and an M (> 1) divided high frequency oscillation signal In the radio frequency modulation apparatus comprising a phase comparison means for outputting the result of the phase comparison, and a charge pump for increasing or decreasing the current in response to the result output from the phase comparison means, and outputs the result of the current increase or decrease A low pass filtering of the output signal of the charge pump, a loop filter for outputting the low pass filtered result as a control voltage, a mutual conductance value adjusted in response to an external switching control signal, and the adjusted result as a mutual conductance adjustment signal. The inductance value is changed in response to the mutual conductance adjustment means and the mutual conductance adjustment signal to be output, and in response to the control voltage. In response, it is preferable that the high frequency oscillator is configured to change the capacitance value and to change the frequency of the high frequency oscillation signal by the changed inductance and capacitance values.

Hereinafter, with reference to the accompanying drawings with respect to the radio frequency modulation apparatus widening the oscillation frequency variable range of the high frequency signal according to the present invention will be described.

Figure 4 is a block diagram of an embodiment for explaining the radio frequency modulation device widening the oscillation frequency variable range of the high frequency signal according to the present invention, a programmable counter 400, prescaler 410, RF oscillator 420, gm adjustment unit ( 430, reference oscillator 440, reference divider 450, phase detector 460, charge pump 470 and loop filter 480.

The reference oscillator 440 of FIG. 4 is generally implemented as a crystal oscillator and generates a reference oscillation signal REF_OSC having a predetermined reference frequency. Here, the reference oscillator 440 may be implemented using a crystal oscillator, and the reference oscillation signal REF_OSC may be 4 MHz.

The reference divider 450 divides the reference oscillation signal REF_OSC output from the reference oscillator 440 at a predetermined rate and outputs the divided signal REF_D. Here, the reference divider 450 preferably divides the reference oscillation signal REF_OSC by 256 to generate a divided signal of 15.625 KHz.

The phase detector 460 inputs the divided high frequency oscillation signal RF_D output from the programmable counter 400 and the divided reference oscillation signal REF_D to compare the phases, and outputs a signal corresponding to the phase compared result. .

The charge pump 470 increases or decreases a predetermined current in response to the signal output from the phase detector 460 and outputs an increased or decreased result.

The loop filter 480 inputs the result output from the charge pump 70 to filter the low pass component, and outputs the result of filtering the low pass component as the control voltage Vt. At this time, the oscillation frequency of the RF oscillator 420 is varied by the output control voltage Vt.

The gm adjustment unit 430 generates different mutual conductance values gm in response to the switching control signal CON applied from an external switch or a microprocessor (not shown), and the gm adjustment signal gm_c. Output as. At this time, the gm adjustment signal gm_c may be referred to as gm control current.

The RF oscillator 420 changes the oscillation frequency of the high frequency signal by the variable capacitance of the varicap diode and the variable inductance value of the coil, and the generated high frequency signal is output as a carrier signal during modulation. In addition, the inductance of the RF oscillator 420 is varied by the gm adjustment signal gm_c output from the gm adjustment unit 430, and the capacitance of the barrier cap diode is changed by the control voltage Vt output from the loop filter 480. The oscillation frequency of the carrier signal RF_OSC is varied. The RF signal RF_OSC generated by the RF oscillator 420 may be oscillated in a frequency range of 40 to 250 MHz.

The prescaler 410 divides the RF signal RF_OSC output from the RF oscillator 420 at a predetermined rate and outputs the divided signal. Here, the prescaler 410 may be set to divide the RF signal RF_OSC by eight.

The programmable counter 400 inputs a signal divided by the prescaler 410 to correspond to each country or channel, and counts in response to a switching control signal CON output from an external switch or a microprocessor (not shown). The value is changed to select a division ratio for re-dividing the divided signal. At this time, the signal divided by the programmable counter 400 is defined as RF_D, and RF_D is applied to the phase detector 460. As an example, the programmable counter 400 may be implemented as a 10-bit counter.

FIG. 5 is a circuit diagram of an exemplary embodiment for explaining the RF oscillator 420 of the RF modulation apparatus shown in FIG. 4 and includes a first oscillator 50 and a second oscillator 55. Here, the first oscillator 50 is implemented as elements provided on the outside of the chip, the second oscillator 55 is implemented as elements embedded in the chip.

In the first oscillator 50 of FIG. 5, the control cap VD and the cathode of the barrier cap diode VD50 are connected, and a capacitor C52 is connected between the anode and the second node N2 of the VD50. In addition, the capacitor C50 is connected between the control voltage Vt and the first node N1. Here, the capacitors C50 and C52 serve to block a DC component applied to the variable coil Lg50. In addition, the capacitance of the barrier cap diode VD50 is changed by the control voltage Vt output from the loop filter 480, that is, the reverse voltage.

In the second oscillator 55 of FIG. 5, the variable coil Lg50 is implemented as a gyrator GYRATOR and is connected between the first node N1 and the second node N2. The amplifier 57 is implemented as a differential amplification circuit which applies and amplifies the voltages of the first node N1 and the second node N2 to the positive input terminal and the negative input terminal, respectively, and amplifies the RF oscillation signal RF_OSC. Output as In the variable coil Lg50, the gm value of the gyrator is changed corresponding to the gm adjustment signal gm_c, thereby changing the inductance value. Here, it is preferable that the voltage amplification degree of the amplifier 57 is one.

As described above, in the present invention, the coil of the high frequency oscillator does not have a fixed inductance, but is implemented as a variable coil that can be varied by a mutual conductance value (gm), and is implemented as a gyrator to be embedded in a chip. There is an advantage that it can.

FIG. 6 is a detailed circuit diagram illustrating the variable coil Lg50 of the RF oscillator 420 illustrated in FIG. 5. The parasitic resistor G1 and the voltage controlled current source VCCS 60 are described below. , A second VCCS 65, a second parasitic resistor G2, and a capacitor C2. Here, the first VCCS 60 includes a first current source I61 connected to a node across the first input voltage v1 and a first voltage source V61 connected across the second input voltage. In addition, the second VCCS 65 includes a second current source I62 connected to a node across the second input voltage v2 and a second voltage source V62 connected across the first input voltage v1.

In practice, it can be seen that the variable coil Lg50 is constituted by the first and second VCCSs 60 and 65 and the capacitor C2. In addition, the voltage source V61 of the first VCCS 60 is equal to the voltage v2 of the second input node, and the voltage source V62 of the second VCCS 65 is equal to the voltage V1 of the first input node. That is, the voltage of the voltage source V61 is changed into a current component through the current source I61, and at this time, the mutual conductance value gm is obtained. In addition, the voltage of the voltage source V62 is changed into a current component through the current source I62, at which time the mutual conductance value gm is obtained. In the gyrator, two gm values obtained in the first VCCS 60 and the second VCCS 65 are designed to be equal to each other.

Therefore, when gm generated in the first VCCS 60 and the second VCCS 65 are the same, the relationship between the input voltages v1 and v2 and the currents i1 and i2 in FIG. same.

Therefore, the input impedance of the gyrator circuit can be obtained as follows by Equation (2).

Here, s represents jw and the phase of the current i1 is delayed by 90 compared with the phase of the input voltage v1 by the reactance characteristic of the coil. Therefore, by the equation (3) the input impedance (Z) is implemented to have the characteristics of inductance, that is, inductor. The inductance of the variable coil Lg50 shown in FIG. 6 may be expressed as follows.

As described above, since the inductance of the variable coil Lg50 shown in FIG. 6 may be changed by the gm value, the oscillation frequency generated by the high frequency oscillator 420 may widen the frequency variable range by the value of Lg50.

That is, in the conventional RF modulation device, the oscillation frequency of the high frequency signal is varied by only changing the capacitance value of the barrier cap diode, but in the present invention, not only the barrier cap diode VD50 but also the variable coil Lg50 embedded in the chip. The inductance value can also be a variable for frequency adjustment. Therefore, in the present invention, the oscillation frequency variable range of the RF signal can be much wider than the conventional case.

As a result, the oscillation frequency signal of the RF oscillator 420 shown in FIG. 5 can be obtained as follows. Here, C2 in the equivalent circuit of FIG. 6 represents the same case as the capacitance of the barrier cap diode VD50 of FIG. 5.

Here, C _VD50 represents the capacitance of the Varicap diode VD50 provided outside the chip, and it can be seen that the frequency of the oscillation signal may vary in proportion to the mutual conductance value gm of the variable coil Lg50. Can be. Therefore, since the oscillation frequency variable range of the high frequency signal is widened, it is possible to cover the range of 40 to 250 MHz which is the frequency band of the carrier signal in the RF VHF band. Therefore, there is an advantage that it is easy to apply to multiple countries, multiple channels.

FIG. 7 is a detailed circuit diagram illustrating the gm adjuster 430 of the RF modulator shown in FIG. 4. Referring to FIG. 7, the gm control unit 430 has one side connected in common with the power supply voltage VCC and a plurality of switches SW71 to SW7n connected in parallel to each other, and the other side of the switches SW71 to SW7n. Each adder 74 includes a current source I71 to I7n connected to one side and an gm value connected to the other side of the current sources I71 to I7n to add gm values output from the respective current sources.

That is, each of the switches I71 to I7n illustrated in FIG. 7 is turned on / off in response to a switching control signal CON applied from an external switch or a microprocessor (not shown), and is connected to the turned-on switch. The gm value is output by.

The adder 74 adds gm values generated from the current sources connected to the switches in the switched on state, and outputs the added result as a gm adjustment signal gm_c.

As described above, in the RF modulation apparatus according to the present invention, the value of the gm adjustment signal gm_c is changed by the switching control signal CON in order to be applied to multiple countries or multiple channels.

According to the present invention, when implementing a high frequency oscillator of an RF modulation device using a PLL, by implementing a variable coil using a gyrator, it is possible to widen the oscillation frequency variable range of the high frequency signal, thereby corresponding to multiple countries and multiple channels It has the effect of being possible. In addition, since the coil of the high frequency oscillator is embedded in the chip, not only can reduce the cost and size of the module, but also improve the productivity by eliminating the problem of variation in inductance (VARIATION) that can occur in the conventional external coil. There is.

Claims (5)

Phase comparison means for outputting a phase-compared result by phase comparing the N (> 1) -divided reference oscillation signal and the M (> 1) -divided high-frequency oscillation signal; A radio frequency modulation device having a charge pump that increases or decreases and outputs a result of increasing or decreasing current, A loop filter for low pass filtering the output signal of the charge pump and outputting the low pass filtered result as a control voltage; Mutual conductance adjustment means for adjusting a mutual conductance value in response to an external switching control signal and outputting the adjusted result as a mutual conductance adjustment signal; And And a high frequency oscillator for changing an inductance value in response to the mutual conductance adjustment signal, for varying a capacitance value in response to the control voltage, and for varying the frequency of the high frequency oscillation signal by the changed inductance and capacitance values. A radio frequency modulation device characterized in that. The method of claim 1, wherein the high frequency oscillator, Oscillation element; A variable coil connected to both ends of the oscillation element and implemented as a gyrator for changing a mutual conductance value by the mutual conductance adjustment signal; A first capacitor connected between the control voltage and one side of the variable coil to block a DC component of the control voltage; A second capacitor having one side connected to the other side of the variable coil to cut off a DC component of the control voltage; A baricap diode having a cathode connected to the control voltage, an anode connected to the other side of the second capacitor, and a capacitance changed by the control voltage; And And amplifying means for inputting and amplifying the voltages at both ends of the variable coil into the positive input terminal and the negative input terminal, respectively, and outputting the amplified result. The method of claim 2, wherein the high frequency oscillator, The following equation; By the frequency of the high frequency oscillation signal is changed, The gm represents the mutual conductance value generated in the variable coil, the C _VD represents the capacitance of the barrier cap diode. The method of claim 1, wherein the mutual conductance adjusting means, A plurality of switches each connected to one side of the power supply voltage and connected in parallel to each other and switched on / off in response to an external switching control signal; And A plurality of current sources each connected to the other side of the switches to generate mutual conductance; And And adding means for adding a plurality of mutual conductance values output from the plurality of current sources, and outputting the added result as the mutual conductance adjustment signal. The method of claim 4, wherein the mutual conductance adjusting means, The switching control signal is changed for each country or channel to generate a mutual conductance adjustment signal having a different value.