Oscillator controlled by voltage mode linear frequency modulation

Abstract

The invention provides a voltage mode linear frequency modulation controlled oscillator. The oscillator comprises a voltage modulation circuit, a reference current generation circuit and an oscillation circuit. The voltage modulation circuit is configured to generate a modulation voltage according to a feedback voltage and a first reference voltage. The reference current generating circuit is coupled to the voltage modulation circuit and is configured to generate a first reference current according to the modulation voltage and a second reference voltage. The oscillation circuit is coupled to the reference current generation circuit and is configured to generate an oscillation signal with an oscillation frequency according to the first reference current, and the oscillation frequency changes according to the modulation voltage. The oscillator can be adopted by the DC-DC voltage converter, and the problem that the oscillator may fail due to too small modulation current is solved.

Description

Technical Field

[0001] The invention relates to an oscillator, in particular to an oscillator controlled by voltage mode linear frequency modulation. Background Art

[0002] When the buck converter is initially started, the output voltage is relatively low, and the inductor current therefore has a large slope, so that the current detection circuit needs time to detect the inductor current. Therefore, when the inductor current operates at a high frequency and has a large slope, the inductor current is difficult to control.

[0003] In order for the sensing control circuit to accurately and efficiently control the inductor current, the buck converter suppresses the changes in the inductor current and the output voltage by modulating the frequency of the oscillator. In addition, when a short circuit occurs at the output of a typical DC-DC converter such as a buck converter, the output will be shorted to ground or to a low power supply voltage. The large voltage difference generated between the input and output causes a strong current to pass through the inductor of the DC-DC converter, which may cause damage to the circuit or malfunction of the back-end circuit.

[0004] In order to reduce the strong inductor current when the voltage level between the output and input terminals is relatively large, it is necessary to frequency modulate the oscillation signal generated by the oscillator of the DC-DC converter. Through frequency modulation, the sensing control circuit can accurately sense the inductor current signal, and thus can more accurately control the inductor current. Common methods include frequency hopping modulation and linear frequency modulation. Summary of the invention

[0005] In the existing linear frequency modulation method, a current mode is used to improve the frequency of the oscillator to suppress the changes in the inductor current and the output voltage. However, in the above method, when the modulation current is too small, the oscillator will not operate normally, so there is a risk of oscillator failure.

[0006] In view of the above prior art, the inventor has developed a voltage-mode linear frequency modulation controlled oscillator to improve the problems faced by the current-mode linear frequency modulation method.

[0007] To achieve the above and other purposes, the present invention provides a voltage-mode linear frequency modulation controlled oscillator, comprising a voltage modulation circuit, a reference current generating circuit and an oscillation circuit. The voltage modulation circuit is configured to generate a modulation voltage according to a feedback voltage and a first reference voltage. The reference current generating circuit is coupled to the voltage modulation circuit and is configured to generate a first reference current according to the modulation voltage and a second reference voltage. The oscillation circuit is coupled to the reference current generating circuit and is configured to generate an oscillation signal having an oscillation frequency according to the first reference current, wherein the oscillation frequency varies according to the modulation voltage.

[0008] In some embodiments, the initial value of the oscillation frequency is determined according to a first reference voltage.

[0009] In some embodiments, a voltage modulation circuit includes: a first transistor coupled to a high power supply voltage; a second transistor coupled to the first transistor and the high power supply voltage respectively; a current source coupled to the second transistor and the high power supply voltage respectively and generates a current; a third transistor coupled to the first transistor and the second transistor respectively; an error amplifier coupled to a feedback voltage and the third transistor respectively; a first resistor coupled to the error amplifier and the third transistor respectively; a second resistor coupled to the current source and generates a first reference voltage when current passes through the second resistor; and a start-up switch circuit, which is configured between the ground and the first resistor and the second resistor, and is controlled by an enable signal to turn on or off the path between the first resistor, the second resistor and the ground.

[0010] In some embodiments, when the startup switch circuit is turned off, the modulation voltage is equal to the high power supply voltage.

[0011] In some embodiments, a ratio of the first transistor to the second transistor is 1:k, a ratio of the first resistor to the second resistor is 1:n, and k and n are positive numbers and are not equal to each other.

[0012] In some embodiments, when the startup switch circuit is turned on, the modulation voltage is equal to the sum of the first reference voltage and the set voltage.

[0013] In some embodiments, the set voltage is k*n*feedback voltage.

[0014] In some embodiments, the reference current generating circuit includes: a fourth transistor, coupled to a high power supply voltage; a fifth transistor, respectively coupled to the high power supply voltage and the fourth transistor; a sixth transistor, respectively coupled to the fourth transistor and the fifth transistor; an error amplifier, respectively coupled to the modulation voltage, the second reference voltage and the sixth transistor, and configured to generate an error amplification signal to the sixth transistor based on the modulation voltage and the second reference voltage; and a third resistor, respectively coupled to the error amplifier and the sixth transistor, and generating a terminal voltage when the second reference current passes through the third resistor.

[0015] In some embodiments, when the fourth transistor and the sixth transistor are turned on, the second reference current passes through the third resistor.

[0016] In some embodiments, when the modulation voltage is greater than the second reference voltage, the terminal voltage follows the voltage value of the second reference voltage.

[0017] In some embodiments, when the modulation voltage is less than the second reference voltage, the terminal voltage follows the voltage value of the modulation voltage.

[0018] Thus, the voltage-mode linear frequency modulation controlled oscillator of the present invention can make the output voltage of the buck converter smoother when initially started compared to the frequency hopping modulation method. Under low output voltage conditions, the voltage-mode linear frequency modulation controlled oscillator of the present invention can effectively suppress the generation of a large inductor current. In addition, the voltage-mode linear frequency modulation controlled oscillator of the present invention will not cause the oscillator to fail to operate normally due to too small modulation current. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of an oscillator according to an embodiment of the present invention.

[0020] Figure 2 is a schematic diagram of a voltage modulation circuit according to an embodiment of the present invention.

[0021] Figure 3 It is a schematic diagram comparing the output voltage and the inductor current of the present invention and the prior art.

[0022] Description of reference numerals:

[0023] 105 Oscillator

[0024] 221, 212 Error amplifier

[0025] 232 Comparator

[0026] 210 Voltage Modulation Circuit

[0027] 214 Start switch circuit

[0028] 220 Reference current generating circuit

[0029] 230 Oscillator Circuit

[0030] 234 Inverter

[0031] 236 Pulse Generator Circuit

[0032] 400, 402, 404, 406 curves

[0033] C S Oscillation capacitor

[0034] CLK oscillation signal

[0035] I B Current Source

[0036] Ir The first reference current

[0037] Is The second reference current

[0038] M1 first transistor

[0039] M2 Second transistor

[0040] M3 The third transistor

[0041] M4 The fourth transistor

[0042] M5 Fifth transistor

[0043] M6 Sixth transistor

[0044] M7 Seventh transistor

[0045] R A1 First resistor

[0046] R A2 Second resistor

[0047] R T The third resistor

[0048] SW1 First switch

[0049] SW2 Second switch

[0050] V r1 First reference voltage

[0051] V r2 Second reference voltage

[0052] V r3 The third reference voltage

[0053] V A1 Node voltage

[0054] V sen Voltage

[0055] V M Modulation voltage

[0056] V RT Terminal voltage

[0057] V EN Enable signal

[0058] V FB Feedback voltage

[0059] V DD High supply voltage DETAILED DESCRIPTION

[0060] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail by referring to the following specific embodiments in conjunction with the accompanying drawings. The description is as follows:

[0061] Please refer to Figure 1 , is a schematic diagram of an oscillator according to an embodiment of the present invention. Figure 1As shown, the oscillator 105 includes a voltage modulation circuit 210 , a reference current generation circuit 220 and an oscillation circuit 230 .

[0062] The voltage modulation circuit 210 is configured to modulate the voltage according to the feedback voltage V FB With the first reference voltage V r1 Generates modulation voltage V M To the reference current generating circuit 220. The first input terminal of the voltage modulation circuit 210 is coupled to the feedback voltage V FB The second input terminal of the voltage modulation circuit 210 is coupled to the first reference voltage V r1 The output terminal of the voltage modulation circuit 210 is coupled to the reference current generation circuit 220 .

[0063] The reference current generating circuit 220 is coupled to the voltage modulation circuit 210. The reference current generating circuit 220 is configured to generate a voltage according to the modulation voltage V M and the second reference voltage V r2 A first reference current Ir is generated.

[0064] The reference current generating circuit 220 includes an error amplifier 221, a fourth transistor M4, a fifth transistor M5, a sixth transistor M6 and a third resistor R T The first input terminal of the error amplifier 221 is coupled to the second reference voltage V r2 The second input terminal of the error amplifier 221 is coupled to the modulation voltage V M The third input terminal of the error amplifier 221 is coupled to the third resistor R T The third resistor R T The other end of the error amplifier 221 is coupled to the ground. The output end of the error amplifier 221 is coupled to the gate of the sixth transistor M6. The source of the fourth transistor M4 is coupled to the high power supply voltage V DD The gate of the fourth transistor M4 is coupled to the drain of the fourth transistor M4 and the gate of the fifth transistor M5. The source of the fifth transistor M5 is coupled to the high power voltage V DD The drain of the fifth transistor M5 is respectively coupled to the comparator 232 of the oscillation circuit 230 and the oscillation capacitor C S The drain of the sixth transistor M6 is coupled to the drain of the fourth transistor M4. The source of the sixth transistor M6 is coupled to the third resistor R T one end.

[0065] The oscillating circuit 230 is coupled to the reference current generating circuit 220. The oscillating circuit 230 is configured to generate an oscillating signal CLK having an oscillating frequency according to the first reference current Ir, wherein the oscillating frequency is determined according to the modulation voltage V M And changes.

[0066] The oscillation circuit 230 includes a comparator 232, an inverter 234, a pulse generator circuit 236, a seventh transistor M7 and an oscillation capacitor C S The first input terminal of the comparator 232 is coupled to the third reference voltage V r3 The second input terminal of the comparator 232 is respectively coupled to the oscillation capacitor C S , the drain of the seventh transistor M7. The output end of the comparator 232 is coupled to the input end of the inverter 234. The output end of the inverter 234 is coupled to the input end of the pulse generator circuit 236. The output end of the pulse generator circuit 236 is coupled to the gate of the seventh transistor M7, and outputs the oscillation signal CLK. The source of the seventh transistor M7 is coupled to ground. In an embodiment, the fourth transistor M4 and the fifth transistor M5 are implemented by P-type MOSFETs, and the sixth transistor M6 and the seventh transistor M7 are implemented by N-type MOSFETs.

[0067] As mentioned above, when the voltage level between the input voltage and the output voltage is relatively large and the voltage converter is not yet in steady state, the frequency modulation is used to suppress the sharp change of the inductor current. In the buck converter, when the output voltage has not yet reached the set voltage, when the output voltage is too small (which means that the feedback voltage V FB The voltage modulation circuit 210 modulates the feedback voltage V FB With the first reference voltage V r1 Modulate to adjust the output modulation voltage V M to the error amplifier 221. When the modulation voltage V M is less than the second reference voltage V r2 , linear frequency modulation control begins.

[0068] The error amplifier 221 generates a voltage V M , the second reference voltage V r2 Output the error amplified signal to the gate of the sixth transistor M6, and control and adjust the sixth transistor M6 so that the terminal voltage V RT Following the modulation voltage V M Or the second reference voltage V r2 When the fourth transistor M4 and the sixth transistor M6 are turned on, the second reference current Is flows through the third resistor R T , to generate terminal voltage V RT When the modulation voltage V M Greater than the second reference voltage V r2 When the terminal voltage V RT Follow the second reference voltage V r2 The voltage value of the modulation voltage V M is less than the second reference voltage V r2When the terminal voltage V RT Following the modulation voltage V M The voltage value makes the oscillation frequency of the oscillation signal CLK output by the pulse generator circuit 236 lower than the final frequency.

[0069] The fourth transistor M4 and the fifth transistor M5 form a current mirror, and the second reference current Is is mapped to the first reference current Ir. The first reference current Ir passes through the oscillation capacitor C S , to charge and generate voltage V sen The comparator 232 generates a voltage according to the third reference voltage V r3 With voltage V sen The comparison signal is output to the inverter 234. The inverter 234 outputs an inverted signal according to the comparison signal to the pulse generator circuit 236. The pulse generator circuit 236 outputs an oscillation signal CLK according to the inverted signal.

[0070] The current value of the first reference current Ir is affected by the second reference current Is. The current value of the second reference current Is is affected by the error amplifier 221, the sixth transistor M6 and the third resistor R T When the first reference current Ir is larger, the oscillation capacitor C S The faster the charging speed, the faster the oscillation frequency of the oscillation signal CLK output by the pulse generator circuit 236. Conversely, when the first reference current Ir is smaller, the oscillation capacitor C S The slower the charging speed, the slower the oscillation frequency of the oscillation signal CLK output by the pulse generator circuit 236. In addition, the initial value of the oscillation frequency is based on the first reference voltage V r1 Decide.

[0071] Please refer to Figure 2 , is a schematic diagram of a voltage modulation circuit according to an embodiment of the present invention. Figure 2 As shown, the voltage modulation circuit 210 includes an error amplifier 212, a first transistor M1, a second transistor M2, a third transistor M3, a current source I B , the first resistor R A1 , the second resistor R A2 And start the switch circuit 214.

[0072] The first input terminal of the error amplifier 212 is coupled to the feedback voltage V FB The second input terminal of the error amplifier 212 is coupled to the source of the third transistor M3. The output terminal of the error amplifier 212 is coupled to the gate of the third transistor M3.

[0073] The source of the first transistor M1 is coupled to the high power voltage V DDThe gate of the first transistor M1 is coupled to the drain of the first transistor M1 and the gate of the second transistor M2. The source of the second transistor M2 is coupled to the high power supply voltage V DD . Current source I B One end is coupled to a high power supply voltage V DD . Current source I B The other end of is coupled to the drain of the second transistor M2. The drain of the third transistor M3 is coupled to the gates of the first transistor M1 and the second transistor M2 respectively. In an embodiment, the first transistor M1 and the second transistor M2 are implemented by P-type MOSFETs, and the third transistor M3 is implemented by N-type MOSFETs.

[0074] The first resistor R A1 One end of the first resistor R is coupled to the source of the third transistor M3. A1 The other end of the second resistor R is coupled to one end of the start-up switch circuit 214, and the other end of the start-up switch circuit 214 is coupled to ground. A2 One end is coupled to the drain of the second transistor M2, the current source I B The second resistor R A2 The other end of the start switch circuit 214 is coupled to one end of the start switch circuit 214, and the other end of the start switch circuit 214 is coupled to the ground. In other words, the start switch circuit 214 is configured to connect the ground and the first resistor R A1 and the second resistor R A2 Between, by the enable signal V EN Control the conduction or disconnection of the first resistor R A1 , the second resistor R A2 The startup switch circuit 214 is composed of a first switch SW1 and a second switch SW2.

[0075] When the enable signal V EN When the control start switch circuit 214 is turned on, the voltage modulation circuit 210 starts to perform linear frequency modulation control. A1 The voltage value is modulated to approximate the feedback voltage V FB . The first reference voltage V r1 is the current source I B * The second resistor R A2 In other words, when the current source I B Through the second resistor R A2 Generate a first reference voltage V r1 . Modulation voltage V M =V r1 +k*n*V FB , since the feedback voltage V FB Approximately the node voltage V A1 , so the modulation voltage V M =V r1+k*n*V A1 In other words, the modulation voltage V M Equal to the first reference voltage V r1 and the set voltage, where the set voltage is k*n*node voltage V A1 , or set the voltage to k*n*feedback voltage V FB The ratio of the first transistor M1 to the second transistor M2 is 1:k, and the first resistor R A1 With the second resistor R A2 The ratio of the first transistor M1 to the second transistor M2 is 1:2.5, and the first resistor R A1 With the second resistor R A2 The ratio is 1:1. In addition, when the enable signal V EN When the control start switch circuit 214 is turned off, the modulation voltage V M Equal to the high supply voltage V DD .

[0076] Please refer to Figure 3 , is a schematic diagram comparing the output voltage and inductor current of the present invention and the prior art. Figure 3 As shown, the horizontal axis represents time, the upper vertical axis represents voltage, and the lower vertical axis represents current. Curve 400 represents the output voltage using the prior art frequency hopping modulation method. Curve 402 represents the output voltage using the linear modulation method of the embodiment of the present invention. It can be found that between about 3ms and 3.2ms, the output voltage using the linear modulation method of the embodiment of the present invention does not have a sudden huge voltage jump phenomenon.

[0077] Curve 404 represents the inductor current using the frequency hopping modulation method of the prior art. Curve 406 represents the inductor current using the linear modulation method of the embodiment of the present invention. It can be found that between about 3 ms and 3.2 ms, the inductor current using the linear modulation method of the embodiment of the present invention is effectively suppressed within a range to avoid damage to the circuit or malfunction of the back-end circuit.

[0078] In summary, the voltage-mode linear frequency modulation controlled oscillator of the present invention can make the output voltage of the buck converter or at the initial startup smoother than that of the frequency hopping modulation method. Under the low output voltage state, the voltage-mode linear frequency modulation controlled oscillator of the present invention can effectively suppress the generation of a large inductor current. In addition, the voltage-mode linear frequency modulation controlled oscillator of the present invention will not cause the problem of the oscillator not being able to operate normally due to the modulation current being too small.

[0079] The present invention has been disclosed in the above with preferred embodiments, but it should be understood by those skilled in the art that the embodiments are only used to describe the present invention and should not be interpreted as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to the embodiments should be considered to be within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the content defined in the claims.

Claims

1. A voltage-mode linear frequency modulation controlled oscillator, characterized in that: include: a voltage modulation circuit configured to generate a modulation voltage according to a feedback voltage and a first reference voltage; a reference current generating circuit, coupled to the voltage modulation circuit, and configured to generate a first reference current according to the modulation voltage and a second reference voltage; and The oscillation circuit is coupled to the reference current generating circuit and is configured to generate an oscillation signal having an oscillation frequency according to the first reference current, wherein the oscillation frequency varies according to the modulation voltage.

2. The voltage-mode linear frequency modulation controlled oscillator according to claim 1, characterized in that: The initial value of the oscillation frequency is determined according to the first reference voltage.

3. The voltage-mode linear frequency modulation controlled oscillator according to claim 1, characterized in that: The voltage modulation circuit comprises: A first transistor coupled to a high power supply voltage; A second transistor, coupled to the first transistor and the high power voltage respectively; A current source, coupled to the second transistor and the high power supply voltage respectively, and generating a current; A third transistor, coupled to the first transistor and the second transistor respectively; an error amplifier, coupled to the feedback voltage and the third transistor respectively; A first resistor is coupled to the error amplifier and the third transistor respectively; A second resistor is coupled to the current source, and generates the first reference voltage when the current passes through the second resistor; and The startup switch circuit is configured between the ground and the first resistor and the second resistor, and is controlled by an enable signal to turn on or off the path between the first resistor, the second resistor and the ground.

4. The voltage-mode linear frequency modulation controlled oscillator according to claim 3, characterized in that: When the startup switch circuit is turned off, the modulation voltage is equal to the high power supply voltage.

5. The voltage-mode linear frequency modulation controlled oscillator according to claim 3, characterized in that: A ratio of the first transistor to the second transistor is 1:k, a ratio of the first resistor to the second resistor is 1:n, and k and n are positive numbers and are not equal to each other.

6. The voltage-mode linear frequency modulation controlled oscillator according to claim 5, characterized in that: When the startup switch circuit is turned on, the modulation voltage is equal to the sum of the first reference voltage and a set voltage.

7. The voltage-mode linear frequency modulation controlled oscillator according to claim 6, characterized in that: The set voltage is k*n*the feedback voltage.

8. The voltage-mode linear frequency modulation controlled oscillator according to claim 3, characterized in that: The reference current generating circuit comprises: a fourth transistor, coupled to the high power supply voltage; a fifth transistor, coupled to the high power voltage and the fourth transistor respectively; a sixth transistor, coupled to the fourth transistor and the fifth transistor respectively; an error amplifier, coupled to the modulation voltage, the second reference voltage and the sixth transistor respectively, and configured to generate an error amplification signal to the sixth transistor according to the modulation voltage and the second reference voltage; and The third resistor is respectively coupled to the error amplifier and the sixth transistor, and generates a terminal voltage when a second reference current passes through the third resistor.

9. The voltage-mode linear frequency modulation controlled oscillator according to claim 8, characterized in that: When the fourth transistor and the sixth transistor are turned on, the second reference current passes through the third resistor.

10. The voltage-mode linear frequency modulation controlled oscillator according to claim 8, characterized in that: When the modulation voltage is greater than the second reference voltage, the terminal voltage follows the voltage value of the second reference voltage.

11. The voltage-mode linear frequency modulation controlled oscillator according to claim 8, characterized in that: When the modulation voltage is less than the second reference voltage, the terminal voltage follows the voltage value of the modulation voltage.

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