TWI646766B - Oscillator and associated direct current-to-direct current converter applying the oscillator - Google Patents

Abstract

An oscillator includes a reference current generating circuit, a modulator circuit, and an oscillating circuit. The reference current generating circuit generates a first reference current. The modulation circuit generates a modulation current according to the first reference current and the feedback voltage, wherein the modulation current is negatively correlated with the feedback voltage. The oscillating circuit receives at least the modulating current and generates an oscillating signal having an oscillating frequency based on at least the modulating current, wherein the oscillating frequency varies according to the modulating current. The oscillator can be used by a DC to DC voltage converter.

Description

Oscillator and associated DC to DC converter using the oscillator

The present invention relates to an oscillator and a DC to DC converter.

Taking the current mode as an example, when the current mode operation of the buck converter or the boost converter is initially started, the output voltage is relatively low, and the inductor current thus has a large slope, so that the current detecting circuit takes time to detect the representation. Inductor current. Therefore, when the inductor current operates at a high frequency and has a large slope, the inductor current can be difficult to control. In order for the sensing control circuit to accurately and efficiently control the inductor current, the buck converter or boost converter suppresses the change in the inductor current and the output voltage by the frequency of the modulating oscillator. In addition, when a short circuit occurs at the output of a typical DC to DC converter such as a buck converter, the output will be shorted to ground or to a low supply voltage. The large voltage level generated between the input and the output causes a strong current to pass through the inductance of the DC to DC converter, which may cause damage to the circuit. In order to reduce the strong inductor current when the voltage level between the output terminal and the input terminal is relatively large, the oscillating signal generated by the oscillator of the DC-to-DC converter needs to be frequency-modulated, wherein the frequency modulation and the sensing control are transmitted. The circuit can suppress current. In addition, the process from start to steady state will be relatively stable by relatively linear frequency modulation compared to frequency hopping.

It is an object of the present invention to provide an oscillator and associated DC to DC converter using the oscillator to thereby solve the aforementioned problems.

According to one embodiment of the invention, an oscillator is disclosed. The oscillator includes a reference current generating circuit, a modulator circuit, and an oscillating circuit. The reference current generating circuit is configured to generate a first reference current. The modulating circuit is coupled to the reference current generating circuit for generating a modulating current according to the first reference current and the feedback voltage, wherein the modulating current is negatively correlated with the feedback voltage. The oscillating circuit is coupled to the modulating circuit for receiving at least the modulating current and generating an oscillating signal having an oscillating frequency according to at least the modulating current, wherein the oscillating frequency changes according to the modulating current.

In accordance with an embodiment of the present invention, a DC to DC converter is disclosed. The DC to DC converter includes an inductor-capacitor circuit, a feedback circuit, and an oscillator. The inductor-capacitor circuit includes at least an inductor and a capacitor, and is configured to receive an inductor current from an input voltage source of the DC to DC converter via at least one switch to provide energy to a subsequent load. The feedback circuit is coupled to the inductor-capacitor circuit for generating a feedback voltage according to the inductor current. The oscillator is coupled to the feedback circuit for generating an oscillating signal according to the feedback voltage, wherein the switch is controlled according to the oscillating signal. The oscillator includes a reference current generating circuit, a modulator circuit, and an oscillating circuit. The reference current generating circuit is configured to generate a first reference current. The modulating circuit is coupled to the reference current generating circuit for generating a modulating current according to the first reference current and the feedback voltage, wherein the modulating current is negatively correlated with the feedback voltage. The oscillating circuit is coupled to the modulating circuit for receiving at least the modulating current and generating an oscillating signal having an oscillating frequency according to at least the modulating current, wherein the oscillating frequency changes according to the modulating current.

These and other objects of the present invention will become apparent to those skilled in the <RTIgt;

Certain terminology is used throughout the specification and claims to refer to the particular features. As those skilled in the art will recognize, manufacturers can reference components by different names. This manual does not specifically distinguish between components with different names but the same functions. In the following description and claims, the terms "including" and "comprising" are used in an open-ended manner and should not be construed as a closed term such as "consisting of." In addition, the term "coupled" is intended to mean an indirect or direct electrical connection. Thus, if one device is coupled to another device, the connection can be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.

As described in the prior art, for a DC to DC converter such as a buck converter or a boost converter, it requires frequency modulation. Figure 1 illustrates a conventional current mode buck converter with a slope compensation mechanism. The current mode buck converter 10 includes an input voltage source 101, a switching circuit 102, an inductor-capacitor circuit 103, a feedback circuit 104, and an oscillator 105. The input voltage source 101 is used to provide an input voltage Vin. Includes a switching circuit 102 out switch SW ₁ and SW _2, out switch SW ₁ and SW ₂ are controlled by pulse width modulation (PWM) signal and an inverted PWM signal, wherein the PWM signal and the inverted PWM signal from the oscillation of the oscillator 105 The signal CLK is generated. The inductor-capacitor circuit 103 includes an inductor L and a capacitor C, wherein the switch circuit 102 stores/releases energy via the inductor current I _L in response to the inductance L of the inductor-capacitor circuit 103, and the released energy is passed through the load current as shown in FIG. The subsequent load of I _load is utilized. The feedback circuit 104 includes resistors R ₁ and R ₂ for generating a feedback voltage V _FB from the inductor N _L to the terminal N ₁ , wherein the terminal N _{1 is} coupled between the resistors R ₁ and R ₂ . When the load current I _load has a significant change, the current mode buck converter 10 cannot immediately stabilize the output voltage V _O , resulting in a change in the feedback voltage V _FB . The current mode buck converter 10 further includes a typical peak current mode controller 106. A typical peak current mode controller 106 includes an error amplifier 116, an adder 126, a slope compensation circuit 136, a comparator 146, a control logic circuit 156, a high side current sensing circuit 166, a resistor R' and a capacitor C'. The error amplifier 116 includes a negative input terminal for receiving the feedback voltage V _FB and two positive input terminals for receiving the soft start voltage Vss and the reference voltage Vref1 for generating at the output of the error amplifier 116. Voltage V _C . The adder 126 is configured to receive the current sensing voltage Vcs and the ramp voltage V _R , wherein the high side current sensing circuit 166 senses the current on the terminal N ₂ to generate the current sensing voltage Vcs, and the ramp voltage V _{R is} determined by the slope compensation circuit 136 is produced. Comparator 146 is operative to generate a comparison signal at its output. The control logic circuit 156 includes an SR latch 156_1, wherein the SR latch 156_1 receives the oscillating signal CLK generated by the oscillator 105 and the comparison signal generated by the comparator 146 to generate a PWM signal and an inverted PWM signal, respectively. Output Q and inverting output And the WM signal and the inverted PWM signal are transmitted to the switching circuit 102 as shown in FIG. The output of the error amplifier 116 is connected to a series resistor R' and a capacitor C', wherein the resistor R' and the capacitor C' constitute a compensation circuit. However, the compensation circuit is not limited to being implemented by the resistor R' and the capacitor C'. Those skilled in the art will appreciate that the compensation circuit can be implemented by different architectures. A current mode buck converter 10 having a slope compensation mechanism should be well known to those skilled in the art.

The present invention focuses on an oscillator 105 having frequency modulation capability to solve the problems mentioned in the prior art. It is noted here that the oscillator 105 disclosed herein is not limited to application to a buck converter as shown in FIG. In other embodiments, the oscillator 105 can alternatively be applied to a boost converter.

2 is a schematic diagram of an oscillator 105 in accordance with an embodiment of the present invention. The oscillator 105 includes a reference current generating circuit 210, a modulator circuit 220, and an oscillating circuit 230. The reference current generating circuit 210 includes transistors MN1, MP1, MP2, and MP3, a resistor R, and an amplifier 211. As shown, the transistors MP1 and MP3 2 constitute a first current mirror for generating a reference current according to the current I _s I _RT, the transistors MP1 and MP2 form a second current for generating a reference current I _RT I _r according to the current mirror. The current I _{RT is} generated by an operational transconductance amplifier (OTA), which consists of an amplifier 211, a transistor MN1, and a resistor R, and constitutes a current source. The operation and characteristics of the OTA should be well known to those skilled in the art, so for the sake of brevity, Details are omitted here. Note here that for modulation purposes, the magnitude of the reference current I _s is configured to be smaller than the magnitude of the reference current _Ir , which means that the width-to-length ratio of the transistor MP3 is configured to be smaller than the net current characteristic. The width-to-length ratio of the transistor MP2, that is, (W _MP3 / L _MP3 ) < (W _MP2 / L _MP2 ). Modulator circuit 220 is configured to generate a modulation current in accordance with the feedback voltage V _FB feedback circuit 104 and the reference current I _s buck converter 10 from the current mode of the I _d. More specifically, the modulator circuit 220 includes a comparator 221, and the comparator 221 is driven by a reference current I _s for comparing the feedback voltage V _FB with the reference voltage Vref4 to generate a modulation current I _d .

The detailed operation and structure of the modulator circuit 220 will be discussed later. The oscillating circuit 230 includes an oscillating capacitor C _s , a transistor Mosc, a comparison circuit 231, and a pulse generator circuit 232. As shown in FIG. 2, one end of the oscillating capacitor C _s is coupled to the reference current I _r , the modulating current I _d , the drain of the transistor Mosc and the input end of the comparison circuit 231 , and the other end of the oscillating capacitor C _s is coupled To a reference voltage (eg, a ground voltage), wherein the oscillating capacitor C _s receives the reference current I _r and the modulating current I _d to generate a voltage Vsense at the input of the comparison circuit 231. The other input terminal of the comparison circuit 231 is coupled to the reference voltage Vref3, and the comparison circuit 231 compares the reference voltage Vref3 with the voltage Vsense and outputs the result to the pulse generator circuit 232. The pulse generator circuit 232 generates an oscillation signal CLK based on the output of the comparison circuit 231. The details of the oscillating circuit 230 are well known to those skilled in the art. Since the present invention focuses on frequency modulation, the detailed operation of the oscillation circuit 230 is omitted here. In the present embodiment, the transistors MP1, MP2 and MP3 are realized by a P-type metal oxide semiconductor field effect transistor (MOSFET), and the transistor MN1 is realized by an N-type MOSFET.

3 is a schematic diagram of a modulator circuit 220 of an oscillator 105 in accordance with an embodiment of the present invention. The modulator circuit 220 includes transistors MP4, MP5, MN2, MN3, and MN4, wherein the transistors MN3 and MN4 form a third current mirror. As shown in FIG. 3, the gate of the transistor MP4 is coupled to the feedback voltage V _FB of the current mode buck converter 10, the drain of the transistor MP4 is coupled to the drain of the transistor MN3, and the source of the transistor MP4 is coupled. Connect to the reference current I _s . In addition, the gate of the transistor MP5 is coupled to the reference voltage Vref4, the drain of the transistor MP5 is coupled to the drain of the transistor MN2, and the transistor MN2 is configured as a resistor by connecting its gate to the drain, the transistor The source of the MP5 is coupled to the reference current I _s . In other embodiments, the transistor MN2 can be implemented by actual resistance, and the invention is not limited thereto. Finally, in parallel to the oscillation transistor MN4 capacitance C (drain of transistor MN4 is coupled to a capacitance oscillating C _{s) s.} Furthermore, the gate of the transistor MN3 is coupled to the gate of the transistor MN4 and the drain of the transistor MN3. In an embodiment, transistors MP4 and MP5 are implemented by P-type MOSFETs, while transistors MN2 - MN4 are implemented by N-type MOSFETs. As described above, when the voltage level between the input voltage Vin and the output voltage V _O is relatively large, frequency modulation is required, and in the buck converter, when the output voltage V _{O is} too small (this means The feedback voltage V _{FB is} relatively small), and frequency modulation is more required. The modulator circuit 220 compares the feedback voltage V _FB with the reference voltage Vref4 to adjust the current received by the oscillating capacitor C _s . More specifically, when the feedback voltage V _{FB is} smaller than the reference voltage Vref4, the transistor MP4 draws more current from the reference current I _s than the transistor MP5, and according to the characteristics of the current mirror, the drain receiving modulation of the transistor MN4 The current I _d , wherein the modulation current I _d is a part of the reference current _{Ir that does} not pass through the oscillation capacitor C _s . Therefore, the oscillation circuit 230 generates the oscillation signal CLK having the oscillation frequency based on the modulation current I _d and the reference current _Ir . Thus, the received oscillation capacitor C _s current is small, so that the oscillation frequency of the oscillation signal CLK is controlled to be slower (lower). When the feedback voltage V _FB becomes large, the transistor MN4 draws less modulation current I _d (that is, the modulation current I _d is negatively correlated with the feedback voltage V _FB ), which means that the oscillation frequency of the oscillation signal CLK changes. Fast (higher).

The feedback voltage VFB and the modulation current I _d. 4 is a schematic view of an embodiment of the present invention according to FIG. As shown in FIG. 4, when the feedback voltage V _{FB is} close to 0V, the modulation current I _{d is} relatively large to alleviate (reduce) the oscillation frequency of the oscillation signal CLK. When the feedback voltage V _{FB is} gradually increased, the modulation current I _{d is} gradually decreased to accelerate the oscillation frequency of the oscillation signal CLK. This can effectively solve the problems mentioned in the prior art. It should be noted that the above embodiment is described by taking a step-down converter as an example. However, the concept of the modulator circuit 220 can also be used to control the oscillation frequency of the oscillation signal CLK applied to the boost converter. For example, when the output voltage of the current mode boost converter is greater than the input voltage, for example, V _O = Vin ~ XVin, where X is a value greater than 1, the oscillating capacitor receives less current to mitigate (reduce) the oscillating signal The oscillation frequency of CLK. In this case, the architecture of the modulator circuit 220 should be slightly adjusted. Those skilled in the art will appreciate the implementation of the modulator circuit 220 applied to the oscillator 105 of the boost converter, and a detailed description is omitted herein for the sake of brevity.

The above are only the preferred embodiments of the present invention, and all changes and modifications made within the scope of the claims of the present invention should fall within the scope of the present invention. Accordingly, the above disclosure should be construed as limited only by the scope of the appended claims.

10‧‧‧ Current Mode Buck Converter

101‧‧‧Input voltage source

102‧‧‧Switch circuit

103‧‧‧Inductance-capacitor circuit

104‧‧‧Feedback circuit

105‧‧‧Oscillator

106‧‧‧Typical peak current mode controller

116‧‧‧Error amplifier

126‧‧‧Adder

136‧‧‧Slope compensation circuit

146, 221‧‧‧ comparator

156‧‧‧Control logic

156_1‧‧‧SR latch

166‧‧‧High-side current sensing circuit

210‧‧‧current generation circuit

211‧‧Amplifier

220‧‧‧ modulator circuit

230‧‧‧Oscillation circuit

231‧‧‧Comparative circuit

232‧‧‧pulse generator circuit

C, C'‧‧‧ capacitor

Cs‧‧‧Oscillation Capacitor

CLK‧‧‧ oscillating signal

I _d ‧‧‧ modulated current

I _RT ‧‧‧current

I _L ‧‧‧Inductor current

I _load ‧‧‧Load current

I _r , I _s ‧‧‧reference current

L‧‧‧Inductance MN1～MN3, MP1～MP5, Mosc‧‧•O crystal

N ₁ , N ₂ ‧‧‧ terminals

PWM‧‧‧PWM signal

‧‧‧Inverted PWM signal

Q‧‧‧output

‧‧‧inverting output

R, R ₁ , R', R ₂ ‧ ‧ resistance

R‧‧‧Reset input

S ‧‧‧Setting input

SW ₁ , SW ₂ ‧‧ ‧ switch

Vin‧‧‧Input voltage

V _O ‧‧‧Output voltage

Vss‧‧‧ soft start voltage

Vref1～Vref4‧‧‧reference voltage

Vc, Vsense‧‧‧ voltage

Vcs‧‧‧ current sensing voltage

V _R ‧‧‧Ramp voltage

V _FB ‧‧‧ feedback voltage

V _DD ‧‧‧High power supply voltage

1 is a schematic diagram of a buck converter according to the prior art; FIG. 2 is a schematic diagram of an oscillator according to an embodiment of the present invention; FIG. 3 is a schematic diagram of a modulator circuit of an oscillator according to an embodiment of the present invention; 4 is a schematic diagram of a feedback voltage and a modulated current according to an embodiment of the present invention.

Claims (11)

An oscillator includes: a reference current generating circuit configured to generate a first reference current; a modulator circuit coupled to the reference current generating circuit, wherein the modulator circuit is configured to use the first reference The current and a feedback voltage generate a modulation current, and the modulation current and the feedback voltage are negatively correlated with each other; and an oscillating circuit coupled to the modulating circuit, wherein the oscillating circuit is configured to receive at least the modulation And generating an oscillating signal having an oscillating frequency according to the modulating current, wherein the oscillating frequency changes according to the modulating current. The oscillator of claim 1, wherein the maximum value of the modulation current is equal to the first reference current. The oscillator of claim 1, wherein the modulator circuit comprises: a first transistor coupled to the first reference current, wherein the first transistor is controlled by the feedback voltage. The oscillator of claim 3, wherein a source of the first transistor is coupled to the first reference current, a gate of the first transistor is coupled to the feedback voltage, and the modulator circuit is The method further includes: a current mirror coupled to a drain of the first transistor to generate the modulated current. The oscillator of claim 3, wherein the modulator circuit further comprises: a second transistor coupled to the first reference current, wherein the second transistor is controlled by a reference voltage. The oscillator of claim 5, wherein a source of the second transistor is coupled to the first reference current, a gate of the second transistor is coupled to the reference voltage, and the modulator The circuit further includes: a resistor circuit coupled to a drain of the second transistor. The oscillator of claim 6 wherein the resistor circuit comprises a third transistor. The oscillator of claim 1, wherein the reference current generating circuit comprises: a current source; a first current mirror coupled to the current source and the modulator circuit, wherein the first current mirror is configured To generate the first reference current; a second current mirror coupled to the current source and the oscillating circuit, wherein the second current mirror is configured to generate a second reference current to the oscillating circuit, the second reference current is greater than The first reference current, and the oscillating circuit generates the oscillating signal according to the modulating current and the second reference current. The oscillator of claim 8, wherein the first current mirror comprises a first transistor, and the second current mirror comprises a second transistor, and a width-to-length ratio of the first transistor Less than a width-to-length ratio of the second transistor. The oscillator of claim 1, wherein the oscillating circuit comprises: an oscillating capacitor; a transistor, wherein a drain of the transistor is coupled to one end of the oscillating capacitor, and a gate of the transistor The first oscillating circuit is coupled to the first input end, the second input end and the output end, the first input end is coupled to the drain of the transistor, and the second input end is coupled a reference voltage; and a pulse generator circuit for generating the oscillating signal based on an output of the output of the comparison circuit. A DC-to-DC converter comprising: an oscillator according to any one of claims 1 to 10; an inductor-capacitor circuit comprising at least an inductor and a capacitor, wherein the inductor-capacitor circuit is configured to pass at least a switch receives an inductor current from an input voltage of the DC to DC converter to provide energy to a subsequent load; and a feedback circuit coupled to the inductor-capacitor circuit, wherein the feedback circuit is configured to be based on the inductor current The feedback voltage is generated; wherein the oscillator is coupled to the feedback circuit, wherein the oscillator is configured to generate the oscillation signal according to the feedback voltage, and the switch controls according to the oscillation signal.