TW201427283A - Voltage controlled oscillator and phase locked loop - Google Patents

Abstract

A voltage controlled oscillator including a voltage generation unit, a first transforming unit, a second transforming unit, a counter and a controlling unit. The voltage generation unit provides different output voltages according to first switching information. The first transforming unit transforms the different output voltages to generate different output currents according to second switching information. The second transforming unit transforms the different output currents to generate different output signals. The counter counts a pulse number of each control signal to generate a control signal. The controlling unit obtains a first digital code and a second digital code according to the control signal and generates the first and the second switching information. The voltage generation unit serves an input voltage as the output voltage and the controlling unit generates the second switching information to adjust the output current according to the first and the second digital codes.

Description

Voltage controlled oscillator and phase-locked loop

The present invention relates to a Voltage Controlled Oscillator (VCO), and more particularly to a voltage controlled oscillator that compensates for changes in slope.

Figure 1 is a schematic diagram of the conversion curve of a voltage controlled oscillator. The horizontal axis is the input voltage of the voltage controlled oscillator, and the vertical axis is the output frequency of the voltage controlled oscillator. The slope of the conversion curve of the voltage controlled oscillator is not stable due to variations in process, voltage, and temperature. As shown in Figure 1, the voltage controlled oscillator has different conversion curves, each of which has a different slope.

In order for the conversion curve to cover a sufficient frequency range, it is known to increase the input voltage of the voltage controlled oscillator. However, external devices may not be able to provide a large voltage to the voltage controlled oscillator. Another solution is to increase the slope of the conversion curve, but the conversion curve with a large slope is susceptible to noise interference, which in turn affects the overall bandwidth and efficiency of the circuit.

The invention provides a voltage controlled oscillator comprising a voltage generating unit, a first converting unit, a second converting unit, a counter and a control unit. The voltage generating unit uses one of a first voltage and a second voltage as an output voltage according to a first switching information. The first converting unit converts the output voltage according to a second switching information to generate an output current. The second conversion unit converts the output current to generate an output signal. count The controller calculates the number of pulses of the output signal to generate a control signal. The control unit generates the first and second switching information according to the control signal. During a first period, the voltage generating unit uses the first voltage as an output voltage, and the control unit learns a first digit value according to the control signal. During a second period, the voltage generating unit uses the second voltage as an output voltage, and the control unit learns a second digit value based on the control signal. During a third period, the voltage generating unit uses an input voltage as the output voltage, and the control unit generates second switching information for adjusting the output current according to the first and second digit values.

In order to make the features and advantages of the present invention more comprehensible, the preferred embodiments are described below, and are described in detail with reference to the accompanying drawings.

Figure 2 is a schematic diagram of the voltage controlled oscillator of the present invention. As shown, the voltage controlled oscillator 200 includes a voltage generating unit 210, converting units 220, 230, a processing unit 240, and a control unit 250. In the present embodiment, the voltage controlled oscillator 200 has a stable slope and does not change greatly with the drift of the process, voltage and temperature, thereby providing better frequency and efficiency.

The voltage generating unit 210 uses one of the voltages V1 and V2 as an output voltage Vco according to the switching signals S0 to S2 of the switching information IM1. The present invention does not limit the internal architecture of the voltage generating unit 210. In this embodiment, the voltage generating unit 210 includes a comparator 211, a P-type transistor 212, a voltage divider 213, and switches 214-216.

The comparator 211 receives a predetermined voltage Vbg and is coupled to the P-type transistor 212 and the voltage divider 213. The P-type transistor 212 and the voltage divider 213 are connected in series between the operating voltages V _DD and GND. The voltage divider 213 has resistors R1 to R3. The resistors R1 to R3 divide the preset voltage Vbg to generate voltages V1 and V2. The switches 214 to 216 use one of the voltages V1, V2, and Vin as the output voltage Vco based on the switching information IM1. In this embodiment, the switching information IM1 has three switching signals S0~S2 for controlling whether the switches 214-216 are turned on or off.

The invention does not limit the number of switching signals. In a possible embodiment, the number of switching signals is related to the type of switches 214-216. For example, if the switches 214-216 are the same type of switches, such as P-type transistors or N-type transistors, the number of switching signals may be the same as the number of switches 214-216.

In other embodiments, if the switches 214-216 are complementary switches, such as the switch 215 is an N-type transistor, and the switch 216 is a P-type transistor, the switches 215 and 216 can be controlled by only one switching signal. . For example, when a switching signal is in a first state (such as a high level), the switch 215 is turned on, and the switch 216 is not turned on. When the switching signal is in a second state (eg, a low level), the switch 216 is turned on and the switch 215 is not turned on.

The converting unit 220 converts the output voltage Vco according to the switching information IM2 to generate an output current Ic. The present invention does not limit the internal circuit architecture of the conversion unit 220. As long as the circuit structure capable of converting a voltage into a current can be used as the conversion unit 220. In the present embodiment, the conversion unit 220 includes a complex current source and a plurality of switches.

For convenience of explanation, FIG. 2 only shows current sources 221 to 223 and switches 224 to 226. The current sources 221 to 223 receive the operating voltage V _DD and generate currents I ₁ to I ₃ according to the output voltage Vco. In this embodiment, the switches 224-226 are coupled to the current sources 221 to 223 one-to-one, and determine whether to output a corresponding current according to the switching information IM2.

The present invention does not limit how the switching information IM2 controls the switches 224-226. In a possible embodiment, the switching information IM2 has three switching signals (not shown) that respectively turn on or off the switches 224-226, but are not intended to limit the present invention. In other embodiments, by controlling the types of switches 224-226, a plurality of switches can be controlled with a smaller number of switching signals. In the present embodiment, when the switches 224 to 226 are both turned on, the output current Ic is the sum of the currents I ₁ to I ₃ . When the switches 224 and 225 are turned on, and the switch 226 is not turned on, the current Ic is output currents I ₁ and I ₂ sum.

The conversion unit 230 converts the output current Ic to generate an output signal Fc. The present invention does not limit the internal circuit architecture of the conversion unit 230. As long as a current circuit capable of converting a current into a frequency can be used as the conversion unit 230. In the present embodiment, the conversion unit 230 has a plurality of oscillating cells (VCO cells) connected in series. For convenience of explanation, FIG. 2 only shows the oscillating cells 231 to 233.

Processing unit 240 generates a control signal Sc based on output signal Fc. The present invention is not limited to the internal architecture of processing unit 240. As long as the hardware circuit capable of converting a frequency into a digital code can be used as the processing unit 240. In this embodiment, the processing unit 240 is a counter 241 for calculating the number of pulses of the output signal Fc according to the switching signals S1 and S2, and using the calculated result as a control signal Sc.

The control unit 250 generates switching information IM1, IM2 based on the control signal Sc. The invention does not limit the internal architecture of the control unit 250. As long as A digital circuit architecture capable of providing suitable switching information can be used as the control unit 250. In a possible embodiment, the reset signal RES is used to reset the processing unit 240 and the control unit 250.

In this embodiment, the control unit 250 causes the voltage generating unit 210 to provide different output voltages by switching the information IM1. Figure 3 is a schematic diagram of the switching information IM1 of the present invention. For convenience of explanation, the switching information IM1 has switching signals S0 to S2, but is not intended to limit the present invention. In other embodiments, the switching information IM1 may utilize other numbers of switching signals to cause the voltage generating unit 210 to provide different output voltages.

In the period T1, the switching signal S1 is in a uniform energy state (e.g., a high level), and therefore, the voltage generating unit 210 uses the voltage V1 as the output voltage Vco. In this embodiment, the control unit 250 turns on all the switches 224-226 in the conversion unit 220 through the switching information IM2. The conversion unit 220 generates a corresponding output current Ic according to the output voltage Vco. The conversion unit 230 converts the output current Ic to generate a corresponding output signal Fc. At this time, the output signal Fc has a frequency F1. Processing unit 240 generates control signal Sc based on frequency F1. The control unit 250 knows a digital value C1 based on the control signal Sc. In a possible embodiment, the processing unit 240 calculates the number of pulses of the output signal Fc and provides the result of the counting to the control unit 250 as a control signal.

In the period T2, the switching signal S2 is at a high level, and therefore, the voltage generating unit 210 uses the voltage V2 as the output voltage Vco. In this embodiment, the control unit 250 turns on all the switches 224-226 in the conversion unit 220 through the switching information IM2. The conversion unit 220 generates a corresponding output current Ic according to the output voltage Vco. The conversion unit 230 converts the output current Ic for A corresponding output signal Fc is generated. At this time, the output signal Fc has a frequency F2. Processing unit 240 generates control signal Sc based on frequency F2. The control unit 250 knows a digital value C2 based on the control signal Sc. In the present embodiment, the processing unit 240 calculates the number of pulses of the output signal Fc, and supplies the result of the counting as a control signal to the control unit 250.

In the period T3, the switching signal S0 is at the high level, and therefore, the voltage generating unit 210 regards the input voltage Vin as the output voltage Vco. In the present embodiment, the control unit 250 generates switching information IM2 for determining the number of switches that are turned on in the conversion unit 220 based on the digital values C1 and C2.

In a possible embodiment, the control unit 250 adjusts the output current Ic of the conversion unit 220 according to the difference ΔC of the digital values C1 and C2. For example, when the difference ΔC is greater than a predetermined value, it indicates that the slope of the conversion curve of the voltage controlled oscillator 200 is too large, and the frequency of the output signal Fc of the conversion unit 230 needs to be reduced. Therefore, the control unit 250 reduces the number of turned-on switches in the conversion unit 220 to reduce the output current Ic and make the output frequency Fc of the conversion unit 230 small.

When the difference ΔC is smaller than the preset value, it means that the slope of the conversion curve of the voltage controlled oscillator 200 is too small, and the frequency of the output signal Fc of the conversion unit 230 needs to be increased. Therefore, the control unit 250 increases the number of turned-on switches in the conversion unit 220 to increase the output current Ic of the conversion unit 220 and causes the frequency of the output signal Fc of the conversion unit 230 to become large.

As shown in FIG. 3, in the period T3, the output signal Fc of the conversion unit 230 has the frequency F3. At this time, the output signal Fc can be used as an output signal of the voltage controlled oscillator 200. In the present embodiment, during the period T3, the processing unit 240 stops the operation, and the control unit 250 fixes the switching information IM1 and IM2.

Figure 4 is an application example of a voltage controlled oscillator of the present invention. In the present embodiment, the voltage controlled oscillator is applied in a phase locked loop (PLL), but is not intended to limit the present invention. In other embodiments, the clock signal generated by the voltage controlled oscillator can also be applied to other electronic circuits. As shown, the phase locked loop 400 includes a phase frequency detector (PFD) 410, a charge pump 420, a low pass filter (LPF) 430, and a voltage controlled oscillator (VCO) 440. And a frequency divider (Divdier) 450.

The phase frequency detector 410 generates a charging signal Up and a discharging signal Dn according to a reference clock Fref and a feedback clock Ffb. The charge pump 420 generates a control voltage Vc according to the charge signal Up and the discharge signal Dn. The low pass filter 430 processes the control voltage Vc for generating an input voltage Vin. The voltage controlled oscillator 440 generates an output signal Fc based on the input voltage Vin. The frequency divider 450 processes the output signal Fc to generate a feedback clock Ffb.

In the present embodiment, the voltage controlled oscillator 200 shown in FIG. 2 can be used as the voltage controlled oscillator 440. Taking FIG. 2 as an example, before the phase-locked loop 400 starts operating, the shilling voltage generating unit 210 uses the voltages V1 and V2 as the output voltage Vco, so that the converting unit 230 generates the output signals Fc of different frequencies. The processing unit 240 generates different control signals Sc according to different frequencies. The control unit 250 knows the corresponding digit value according to the different control signal Sc, and determines the number of the turned-on switches of the conversion unit 220 by using the difference between the two digit values.

Since the voltage controlled oscillator 440 itself has an adjustment function, it can generate an appropriate switching slope based on the detected switching slope. Since the voltage controlled oscillator 440 can provide a relatively stable conversion slope, it is difficult to follow Changes in process, voltage, and temperature. Therefore, when the phase locked loop 400 starts to operate, the voltage controlled oscillator 440 can provide an optimum switching slope, thereby making the settling behavior of the phase locked loop 400 relatively stable and without greatly increasing the complexity of the circuit. .

Unless otherwise defined, all terms (including technical and scientific terms) are used in the ordinary meaning Moreover, unless expressly stated, the definition of a vocabulary in a general dictionary should be interpreted as consistent with the meaning of an article in its related art, and should not be interpreted as an ideal state or an overly formal voice.

Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

200, 440‧‧‧ voltage controlled oscillator

210‧‧‧Voltage generating unit

220, 230‧‧‧ conversion unit

240‧‧‧Processing unit

250‧‧‧Control unit

211‧‧‧ comparator

212‧‧‧P type transistor

213‧‧ ‧ Voltage divider

214~216, 224~226‧‧‧ switch

221~223‧‧‧current source

231~233‧‧‧ oscillating cell

IM1, IM2‧‧‧ Switching information

V1, V2‧‧‧ voltage

Vco‧‧‧ output voltage

Vbg‧‧‧Preset voltage

R1~R3‧‧‧ resistor

V _DD , GND‧‧‧ operating voltage

S0~S2‧‧‧Switching signal

Ic‧‧‧Output current

I ₁ ~I ₃ ‧‧‧ Current

Fc‧‧‧ output signal

Sc‧‧‧ control signal

RES‧‧‧Reset signal

During the period of T1~T3‧‧

F1~F3‧‧‧ frequency

400‧‧‧ phase-locked loop

410‧‧‧ phase frequency detector

420‧‧‧Charging pump

430‧‧‧ low pass filter

450‧‧‧Delephone

Fref‧‧‧ reference clock

Ffb‧‧‧Restoration clock

Up‧‧‧Charging signal

Dn‧‧‧discharge signal

Vc‧‧‧ control voltage

Vin‧‧‧Input voltage

241‧‧‧ counter

Figure 1 is a schematic diagram of the conversion curve of a voltage controlled oscillator (VCO).

Figure 2 is a schematic diagram of the voltage controlled oscillator of the present invention.

Figure 3 is a schematic diagram of one of the switching information of the present invention.

Figure 4 is an application example of a voltage controlled oscillator of the present invention.

200‧‧‧Variable Control Oscillator

210‧‧‧Voltage generating unit

220, 230‧‧‧ conversion unit

240‧‧‧Processing unit

250‧‧‧Control unit

211‧‧‧ comparator

212‧‧‧P type transistor

213‧‧ ‧ Voltage divider

214~216, 224~226‧‧‧ switch

221~223‧‧‧current source

231~233‧‧‧ oscillating cell

IM1, IM2‧‧‧ Switching information

V1, V2‧‧‧ voltage

Vco‧‧‧ output voltage

Vbg‧‧‧Preset voltage

V _DD , GND‧‧‧ operating voltage

R1~R3‧‧‧ resistor

S0~S2‧‧‧Switching signal

Ic‧‧‧Output current

I ₁ ~I ₃ ‧‧‧ Current

Fc‧‧‧ output signal

Sc‧‧‧ control signal

RES‧‧‧Reset signal

Vin‧‧‧Input voltage

241‧‧‧ counter

Claims (10)

A voltage-controlled oscillator includes: a voltage generating unit that uses one of a first voltage and a second voltage as an output voltage according to a first switching information; and a first converting unit according to a second switching information Converting the output voltage to generate an output current; a second converting unit converting the output current to generate an output signal; and a counter calculating a number of pulses of the output signal for generating a control signal; a control unit, according to the control signal, generating the first and second switching information; wherein, in a first period, the voltage generating unit uses the first voltage as the output voltage, and the control unit is configured according to the control signal, Knowing a first digit value; in a second period, the voltage generating unit uses the second voltage as the output voltage, and the control unit learns a second digit value according to the control signal; The voltage generating unit uses an input voltage as the output voltage, and the control unit generates the second cut according to the first and second digit values. Information for adjusting the output current. The voltage controlled oscillator of claim 1, wherein the control unit generates the second switching information according to a difference between the first and second count values during the third period. The voltage controlled oscillator of claim 2, wherein the first conversion unit comprises: The plurality of current sources generate a complex current according to the output voltage; the plurality of switches are coupled to the current sources one-to-one, and output corresponding currents according to the second switching information. The voltage controlled oscillator of claim 3, wherein the second switching information turns on the switches during the first and second periods. The voltage controlled oscillator of claim 3, wherein, in the third period, when the difference is greater than a predetermined value, the control unit reduces the output current through the second switching information; When the difference is less than the preset value, the control unit increases the output current through the second switching information. The voltage controlled oscillator of claim 1, wherein the voltage generating unit comprises: a voltage divider that generates the first and second voltages according to a predetermined voltage; and a first switch according to the first Outputting the first voltage according to the switching information; and outputting the second voltage according to the first switching information, wherein the second switch does not output the first switch when the first switch outputs the first voltage a second voltage; when the second switch outputs the second voltage, the first switch does not output the first voltage. The voltage controlled oscillator of claim 6, wherein the first switching information comprises a switching signal, and when the switching signal is in a first state, the first switch outputs the first voltage; when the switching When the signal is in a second state, the second switch outputs the second voltage. The voltage controlled oscillator of claim 6, wherein the first switching information comprises a first switching signal and a second switching signal, and when the first switching signal is in a consistent energy state, the first switch Output the first a voltage; the second switch outputs the second voltage when the second switching signal is in the enabled state. The voltage controlled oscillator of claim 1, wherein the counter stops operating during the third period, and the control unit fixes the first and second switching information. A phase locked loop includes: a phase frequency detector, in the third period, generating a charging signal and a discharging signal according to a reference clock and an output signal; and a charge pump according to the charging and discharging signals a control voltage is generated; a low-pass filter is processed to generate the input voltage; and the voltage-controlled oscillator of claim 1 is generated according to the input voltage, and the output signal is generated according to the input voltage; And a frequency divider, the output signal is processed to generate the feedback clock.