KR900004198B1 - Voltage controled oscillator with high speed current switching - Google Patents

Abstract

The VCO includes a reference capacitor which is charged and discharged by current source and sink output transistors. The output transistors are connected to control transistors in a current mirror fashion with current through the control transistors being maintained at a level proportional to the value of a control input voltage. The control transistors are selectively connected to the output transistors in a current mirror configuration to provide either current source or sink operation. Transmission gates are connected between the gates of the output and control transistors and selectively closed to render the proper output transistor conductive to achieve source or sink operation.

Description

Voltage controlled oscillator with fast current switching

1 is a schematic diagram of an oscillator regulated by a voltage in accordance with the present invention.

2a-2g are timing diagrams related to the present invention;

* Real names of symbols on the main parts of the drawings

10: reference capacitor 12: charging circuit

14 divider circuit 18 voltage-to-current converter

20: input resistor 22: operational amplifier (OP AMP)

24: Pyreback (feedback) resistor 26: Output resistor

28: bias resistor 32: field effect transistor

42,44: transmission gate 72: inverter.

The present invention relates to an oscillator controlled by a voltage (VCO'S), and more particularly, to an oscillator controlled by a voltage which makes an auxiliary metal oxide silicon field effect transistor (CM0S) circuit unified. Oscillators controlled by voltages are widely used in phase locked loop (PLL) circuits.

The voltage controlled oscillator operates to provide an output frequency that is linear to the control input voltage. This is achieved by providing a capacitor that is charged and discharged at a rate proportional to the control voltage. The comparator is provided to switch between charge and discharge, respectively, when the voltage at the capacitor goes above or below the first and second reference voltages.

Oscillators regulated by a voltage, including a current source and a current sink for charging and discharging capacitors, are issued to Hsiao, No. 3,886,408, issued to Takaahashi. 3,904,988, 4,263,567 to Astle and 4,321,561 to Payne and others. In the Peine and Hassiao patents, current switching is provided by a switching transistor located in the output current path. Such circuits are generally acceptable, but the inclusion of switching in the output current path introduces parasitic resistance and vibration capacity and is therefore limited to slowing down the switching time. In order for the VCO to operate normally, it is desirable to allow the current sink or source to be switched as soon as possible to achieve a uniform charge rate for the capacitor. Prior art circuits, including switching in the output current path, make it impossible to achieve such fast switching.

The present invention relates to an oscillator controlled by a voltage having a high switching speed. The voltage controlled oscillator of the present invention is operable at 10 MHz or higher and is therefore suitable for use in phase locked loops of hard disk data separators. The circuit includes a reference capacitor charged and discharged by an output transistor that operates with a current fraction and current sink. The output transistor is connected to the control transistor in the current reflecting arrangement by a transfer gate that opens and closes to regulate the operation of the current source or current sink. The FET capacitor is connected to the gate of the current reflecting transistor so that the output transistor can be opened and closed rapidly. This ensures a uniform charge and discharge rate to the capacitor and ensures accurate oscillation behavior.

The present invention will be described below in accordance with the accompanying drawings. The following description is the most suitable method for carrying out the present invention, which is for the purpose of describing the general principles of the invention only and should not be taken in any sense of limitation. The scope of the invention is best determined by reference to the appended claims.

In FIG. 1, the present invention relates to an oscillator for providing a periodic output signal VCO whose frequency is adjusted by the magnitude of the input control voltage Vc. The reference capacitor 10 is charged and discharged between two reference voltages under the control of the charging circuit 12. The reference voltage is provided by the voltage divider circuit 14 and its output is provided to the comparator 16 which compares the reference voltage to the voltage applied to the reference capacitor 10.

The charging and discharging rate of the circuit is controlled by the control input voltage Vc, which is converted into a control current by a voltage-to-current converter 18. The voltage-current converter is input Resistor 20, operational amplifier 22, feedback resistor 24, output resistor 26 and bias resistor 28. The operating point of the oscillator is determined by the external resistor 30 selected to provide the required control current level Ic corresponding to the given input voltage.

The control current Ic is supplied to and drives the reference N type FET transistor 32. Therefore, the magnitude of the reference current flowing through the transistor 32 depends on the magnitude of the control input voltage. The transistor 32 is connected to the N type transistor 34 in the current reflecting structure. Because of the common connection of the gate and source of the transistor, the current flowing through transistor 34 will reflect the current flowing through transistor 32. The current flowing through the transistor 34 will also flow through the P-type transistor 36 whose drain and gate are connected to the drain of the transistor 34 and to the sourced device Vcc. The current will thus flow through the transistors 34 and 36 and have a magnitude determined by the magnitude of the reference current flowing through the transistor 32.

Gates of transistors 34 and 36 are connected to each of the gates of output transistors 38 and 40 through transfer gates 42 and 44. The source of transistor 38 is connected to ground, the source of transistor 40 is connected to an electrical device, and the drains of these transistors are interconnected to one terminal of reference capacitor 10. Transistor 38 is thus connected to transistor 34 in a current mirror structure, and transistor 40 is coupled to transistor 36 in a current reflection structure.

Transistors 38 and 40 are selectively opened and closed to regulate the charge and discharge of the reference capacitor 10. In order to charge the capacitor 10, the transfer gate 44 is closed to connect the transistor 36 to the transistor 40. In this way, the transistor 40 will operate, allowing current to flow through the transistor and charging the reference capacitor 10.

When charging is complete, the transfer gate 44 is opened and the transfer gate 46 is closed to turn off the transistor 40. FET transistor 48 is connected to the gate of transistor 36 to ensure accurate and rapid switching of transistor 40. Such capacitors store charge and provide sufficient instantaneous current to rapidly switch transistor 40 to a conducting state. In an embodiment of the present invention, the capacitor 48 has a size of approximately 30 picolites (pF) and is biased at a gate-source voltage of 3.5 volts. Transistor 40 is approximately ten times the size of transistor 36, and the current through transistor 40 is proportional to the current through transistor 36 and directly related to the relative size of the transistors.

Thus, a current proportional to the control input voltage will flow through the transistor 36 and the transistor 40 will quickly switch to the conduction state by closing the transfer gate 44. Therefore, the current through the transistor 40 will be cascaded to a level proportional to the control input voltage. This current level will determine the charge rate of the capacitor 10.

Transistor 40 operates as a current source, while transistor 38 operates as a current sink to discharge the reference capacitor 10. The transistor is made conductive by closing the transfer gate 42 to interconnect the gate of transistor 38 with the gate of transistor 34. The size of transistor 38 is approximately ten times the size of transistor 34, and the current flowing through transistor 38 will be proportional to the current flowing through transistor 34. The MOS capacitor 50 is again provided so that sufficient instantaneous current is available to rapidly switch the transistor 38 to the conductive state. One terminal of the capacitor is connected to an integrated device to bias the capacitor 50 to achieve proper M0S capacitor operation. The size of the condenser 50 is equal to the size of the condenser 48, i.e., approximately 30 picofarads pF in the embodiment of the present invention. An additional transfer gate 52 is provided to connect the gate of transistor 38 to ground to turn off the transistor.

High and low reference voltages (3 volts and 2 volts in the embodiment of the present invention) are provided by a voltage divider comprising five interconnected transistors 54, 56, 58, 60 and 62. One of the two reference voltages is provided to the reverse input of the comparator 16 by appropriately adjusting the two transfer gates 64 and 66. The transfer gates are alternately switched and MOS capacitors 68 and 70 are provided to facilitate changing the magnitude of the reference voltage applied to the comparator 16 quickly.

The operation of the oscillator controlled by the voltage of FIG. 1 will be described with reference to the timing diagram of FIG. Initially, the transfer gate 64 is closed and the transfer gate 66 is open, so the reference voltage applied to the reverse input of the comparator 16 is 3 volts as shown in FIG. 2A. The transistor 40 is large, the current through the transistor is positive and its magnitude is determined by the magnitude of the input control voltage. Therefore, the capacitor 10 will be charged at a constant rate determined by the magnitude of the current flowing through the transistor 40 as shown in FIG. 2D.

의 상태를 변경시키는 때까지 계속된다.When the voltage at the capacitor 10 reaches 3 volts, the output of the comparator 16 will change state (Figure 2e), which outputs a first inverter 72 to provide a VCO output. Is applied. Repair of this output 72 is provided by inverter 74. These outputs are provided to the transfer gates 42, 44, 46, 52, 64 and 66, by switching the outputs so that the transfer gate 44 is open and the transfer gate 46 is closed. The transistor 40 is stopped. At the same time, the transfer gate 42 is closed and the transfer gate 52 is open to make the transistor 38 conductive. Therefore, the capacitor 10 starts to discharge through the transistor 38. In addition, the transfer gate 66 is closed and the transfer gate 64 is opened to change the reference voltage applied to the comparator from the 3-volt level to the 2-volt level as shown in FIG. 2A. As shown in FIG. 2C, a step change in the current flowing through the transistor 38 causes the capacitor to discharge at a constant rate as shown in FIG. 2D. This discharge reaches the 2 volt level so that the output of the comparator 16 begins to change as shown in Figure 2e and thus the output signal VCO and the output as shown in Figures 2f and 2g.

It continues until you change its state.

The provision of the capacitors 48 and 50 enables the step change as shown in FIGS. 2B and 2C and the current flowing through the transistors 40 and 38 to be achieved. In addition, capacitors 68 and 70 allow for step changes in the reference voltage between the 3-volt and 2-volt levels to be achieved. As a result, the charge and discharge rates can be controlled very precisely, and accurate oscillation behavior can be achieved at the extremely high frequencies required for many applications, such as those used in the phase-locked loop data separator of disk drives. The reference capacitor will be charged and discharged between the two reference voltages, and the rate of charge can be accurately controlled thanks to the rapid switching of the transistors 38 and 40.

Claims (14)

A) a reference capacitor that is periodically charged and discharged; b) a comparison means for comparing the voltage of the existing capacitor with the first reference voltage when the capacitor is charged and the second reference voltage when the capacitor is discharged. This is the output of the oscillator, and switches from the first level to the second level when the voltage at the capacitor is equal to the first reference voltage, and from the second level when the voltage at the capacitor is equal to the second reference voltage. Comparison means switched to one level, and c) a first M0S transistor and a reference capacitor for discharging the reference capacitor by means of a pump for periodically charging and discharging the reference capacitor at a rate determined by the magnitude of the input voltage. A second auxiliary MOS transistor for charging a third and fourth auxiliary MOS such that a current flowing through the transistor corresponds to a magnitude of an input voltage; A transistor, switching means for alternately connecting the gates of the first and third transistors together to operate the first transistor and alternately connecting the gates of the second and fourth transistors together to operate the second transistor, the third And pump means including first and second capacitors respectively connected to the gates of the fourth transistor and storing charges to facilitate rapid operation of the first and second transistors. And c) a voltage controlled oscillator comprising: a. The method of claim 1, wherein the pump means includes an input means for receiving an input voltage and providing a corresponding control current, wherein the control current described above regulates the amount of current flowing through the third and fourth transistors. Voltage controlled oscillator. 3. The apparatus of claim 2, wherein the input means receives a input voltage and converts the input voltage into an output current, a bias resistor connected between the electric device and the converter, and a gate electrode connected to the output of the first electrode and the converter. M0S control transistor having a current flowing through the control transistor equal to the sum of the current flowing through the bias resistor and the output current, the control transistor gate electrode is connected to the gate electrodes of the third and fourth transistors to provide a current reflecting structure And a M0S control transistor such that a current flowing through the third and fourth transistors corresponds to a current flowing through the control transistor. 2. The device of claim 1, wherein the switching means comprises a first transfer gate coupled between the gates of the first and third transistors and a second transfer gate coupled between the gates of the second and fourth transistors, the transfer gates being the first And alternately closed and open to alternately turn on and off the second transistor. 5. The device of claim 4, further comprising a third transfer gate coupled between the gate of the first transistor and ground, wherein the third transfer gate is closed when the first transfer gate is opened, and between the gate and the transferred device of the second transistor. A fourth transmission gate, wherein the fourth transmission gate is closed when the second transmission gate is opened, and the third and fourth transmission gates described above facilitate the quick stop of operation of the first and second transistors. Voltage controlled oscillator, characterized in that. The voltage controlled oscillator of claim 1, wherein the first and second capacitors are MOS capacitors. The method of claim 6, wherein the first capacitor has a terminal connected to the gate of the third transistor and a terminal connected to the power supply, the second transistor has a terminal connected to the gate of the fourth transistor and a terminal connected to ground. Voltage controlled oscillator. 2. The apparatus of claim 1, wherein the comparing means comprises: voltage switching means for connecting the first and second reference voltages to one reference voltage, a reference capacitor connected to one input of the comparator and the reference terminal connected to the other input of the comparator And a comparator in which the output of the comparator changes state to a frequency determined by the input voltage and the switching means and the voltage switching means are switched in response to a change in the comparator output. 9. The apparatus of claim 8, wherein the reference voltage means comprises a plurality of MOS transistors connected in series with a diode structure between the power supply and ground, wherein the first reference voltage is obtained at one output terminal of the transistor and the second reference voltage is another. A voltage controlled oscillator characterized by being obtained at the output terminal of a transistor. The method of claim 9, wherein the reference voltage means comprises a third capacitor connected to the output terminal of the above-described transistor and a fourth capacitor connected to the output terminal of the another transistor described above, wherein the third and fourth capacitors A voltage controlled oscillator for facilitating fast switching at a reference terminal between a first reference voltage and a second reference voltage. A) an electric device, b) an input means for providing a control current corresponding to the input voltage, c) a high speed switching current pump means for providing a current sink or source, wherein the current magnitude at the output terminal is a function of the control current. A first MOS transistor of a first conductivity type having a first electrode connected to a power supply, a second electrode connected to an output terminal, and a control electrode, a first electrode connected to ground, a second terminal connected to an output terminal, and a control terminal A second MOS transistor of a second conductivity type having a first MOS transistor having a first conductivity type having a first electrode connected to a power supply, a second electrode and a control electrode connected to a second electrode, a first electrode connected to ground, A second electrode connected to the second electrode of the third transistor, a control electrode driven by the input means, the same current of the level determined by the control current being the third and fourth A fourth MOS transistor configured to flow through the transistor, a first capacitor having a terminal connected to the control terminal of the third transistor and storing charge, and a second capacitor having one terminal connected to one terminal of the fourth transistor and storing charge And (a) connecting the control terminal of the first transistor to the control terminal of the third transistor so that a current proportional to the control current flows through the first transistor to the output terminal, or (b) controlling the second transistor. The aforementioned pump means including first switching means for connecting a terminal to a control terminal of the fourth transistor so that a current proportional to the control current flows through the second transistor to the output terminal; d) one terminal connected to the output terminal; And a reference terminal having another terminal connected to ground and ground, which are alternately charged by the first transistor and discharged by the second transistor, G) reference voltage means for providing a first reference voltage and a second reference voltage less than the first reference voltage, f) a comparison means having a first input connected to the output terminal and a second input connected to the reference voltage means; Second switching means for connecting the first or second reference voltage to the comparing means, wherein the first and second switching means described above are adjusted by the output of the comparing means such that the reference capacitor continues to charge to the first reference voltage And a second switching means such that the rate of charging and discharging is controlled by the control current, and the output of the comparing means is the output of the oscillator. a) a biased device, b) a voltage-to-current converter for receiving a control voltage and converting the received control voltage into a control current commercially available at the first node, c) a bias resistor coupled between the powered device and the first node. A bias resistor, where the bias current flows through the bias resistor and is combined with the control current to provide a reference current at the first node, d) the drain is connected to the first node, the source is connected to ground, and the gate and drain are A reference N type MOS transistor intended to be interconnected, wherein the reference N type MOS transistor as reference current flows through such a reference transistor, e) an N type MOS with a gate connected to the ground and a gate connected to the gate of the reference transistor. A second transistor, an N-type MOS second transistor in which a current proportional to the reference current flows through the second transistor, f) A P-type MOS third transistor whose source is connected to the conveyed device, whose drain is connected to the drain of the second transistor, and whose gate and drain are interconnected, with the current flowing through the third transistor flowing through the second transistor. A P-type MOS third transistor, such as g) a first MOS capacitor having a first terminal connected to the gate of the second transistor and a second terminal connected to one of the electrically connected device and ground, and h) at the gate of the third transistor. A second MOS capacitor having a first terminal connected thereto and a second terminal connected to one of the power supply and ground, i) a first MOS switch means having a first terminal and a second terminal connected to the gate of the second transistor, j) a third transistor A third second MOS switch means having a first terminal connected to a gate of the second terminal and a second terminal, k) an N-type MOS fourth connected to a source and a gate connected to a second terminal of the first switch means 1) a third MOS switch means having a first terminal connected to the gate of the fourth transistor and a second terminal connected to the ground; m) a source connected to the power supply and a gate connected to the second terminal of the second switch means. P-type MOS fifth transistor, wherein the P-type MOS fifth transistor of the bar where the drain of the fifth transistor is connected to the drain of the fourth transistor at the pump node, n) one terminal connected to the gate of the fifth transistor A fourth MOS switch having a second terminal connected to o) a reference capacitor having one terminal connected to ground and the other terminal connected to the pump node, p) a capacitor having a first input and a second input connected to the pump node, q Reference voltage means for providing a first reference voltage and a second reference voltage lower than the first reference voltage, r) fifth MOS switch means for selectively adapting the first reference voltage to a second input of the capacitor, s) 2 Set the reference voltage 6M0S switch means for selectively applying to the second input of the capacitor, wherein the switch means described above is adjusted in accordance with the output state of the comparator, and the first, fourth and sixth switch means are opened during the first period. By closing the second, third and fifth switch means, the fifth transistor is quickly operated at a current level proportional to the current flowing through the third transistor, and the reference is applied until the voltage across the fifth transistor is equal to the first reference voltage. The capacitor is charged, and during the second period, each switch means switches off the fifth transistor and switches the fourth transistor to operate at a current level proportional to the current flowing through the second transistor. Discharge the reference capacitor until the voltage equals the second reference voltage, and then switch again to compare The output of the voltage-controlled oscillator, characterized by Sikkim change the state to the frequency corresponding to the magnitude of the control voltage. 13. The voltage controlled oscillator of claim 12 wherein the bias resistor and reference capacitor are external components and the remaining components are on a single integrated circuit of complete integrity. 13. The voltage controlled oscillator of claim 12 wherein the switch means is a transfer gate.

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