CN102970008A - Rapid transient response pulse duration modulation circuit - Google Patents

Abstract

The invention discloses a rapid transient response pulse duration modulation circuit which comprises a PWM(pulse-width modulation)modulator, an incline compensation circuit, a current detecting circuit as well as an error amplifier, wherein the current detecting circuit comprises an LX voltage transferring circuit and a detecting current generator; the output end of the LX voltage transferring circuit is connected with the input end of a detecting current generator, and the PWM modulator comprises a voltage-current comparator, an amplifying circuit and a shaping circuit; the incline compensation circuit adopts a segmental incline compensation structure which converts incline voltage into a current for stacking and comparison, the input end of the voltage-current comparator is respectively connected with the detecting current generator, the error amplifier and the output signal of the incline compensation circuit; and the output end of the voltage-current comparator is connected with the input end of the amplifying circuit, the output end of the amplifying circuit is connected with the input end of the shaping circuit, and the output end of the shaping circuit can output a signal for a PWM modulation circuit.

Description

A kind of fast transient response pulse width modulation circuit

Technical field

The present invention relates to supply convertor, particularly at a kind of fast transient response pulse width modulation circuit of IC interior, belong to microelectronics technology.

Background technology

In system-on-chip designs, power supply plan adopts the dynamic electric voltage adjustment technology can reduce the power consumption of whole system, and this specification requirement output voltage is variable, and can adjust fast.Traditional peak electricity flow pattern DC-DC transducer because it has faster transient response and simple compensating circuit, is better than the major control mode that voltage-type control becomes power supply chip always.The topological structure of peak electricity flow pattern, basic topology as shown in Figure 1, core, the inside is exactly pulse-width modulator, i.e. the PWM modulator.The main signal that receives signal, current detection signal and the error amplifier (EA) of slope compensation of PWM modulation carries out calculation process and then obtains the pulse width modulating signal that system needs.Generally need complicated voltage to turn electric current, electric current supercircuit and a comparator circuit.Because to the needs that at a high speed voltage switches, complicated topological constraints the raising of speed.

Summary of the invention

The objective of the invention is in order to solve traditional DC-DC power supply chip, owing to the delay time that PWM modulator, electric current detecting structure complexity are brought is long, the slow problem of transient response when causing output voltage to switch.For this reason, the invention provides a kind of fast transient response pulse width modulation circuit, with the electric current I of EA output end voltage conversion _EAElectric current I with the conversion of slope compensation voltage _SC, current detection circuit output electric current I _CSAnd compare, when both had intersection point, circuit overturn.Current detection circuit adopts unconventional nonlinear organization, can obtain detecting the function expression of electric current I cs and inductive current IL.The compensation slope was 0 section linear compensating when slope compensation had been taked little duty ratio, load capacity and transient response that can the Effective Raise system.

Above-mentioned purpose of the present invention is achieved through the following technical solutions: a kind of fast transient response pulse width modulation circuit, based on peak electricity flow pattern DC-DC converter topologies, comprise the PWM modulator, current detection circuit, slope compensation circuit and error amplifier, the PWM modulator receives the signal of slope compensation, the signal of current detection signal and error amplifier, carry out calculation process and then obtain the pulse width modulating signal that system needs, it is characterized in that: current detection circuit comprises LX voltage transfer circuit and detects current generator that the output of LX voltage transfer circuit is connected with the input that detects current generator; The PWM modulator comprises voltage-to-current comparator, amplifying circuit and shaping circuit, slope compensation circuit adopts ramp voltage is converted into electric current stack segmentation slope compensation structure relatively, the input of voltage-to-current comparator connects respectively the output signal that detects current generator, error amplifier and slope compensation circuit, the output of voltage-to-current comparator connects the input of amplifying circuit, the output of amplifying circuit connects the input of shaping circuit, the output of shaping circuit is PWM modulation circuit output signal, wherein:

In the current detection circuit, LX voltage transfer circuit comprises switching tube MP1 and PMOS pipe M1, and the source electrode of MP1 connects supply voltage, the grid of MP1 connects control voltage Vcontrol1, the drain electrode of MP1 connects the source electrode of M1, and the grid of M1 meets control signal Vcontrol2, and the drain electrode of M1 is output; Detect current generator and comprise PMOS pipe M2～M5, NMOS pipe M6～M7 and bias current Ibias1, the grid of M2 meets control signal Vcontrol3, the source electrode of M2 connects supply voltage, the drain electrode of M2 connects the source electrode of M3 and the drain electrode of the M1 in the LX voltage transfer circuit, the drain electrode of M3 connects the grid of bias current Ibias1 and M3, M5, the other end ground connection of bias current Ibias1, the source electrode of M5 links to each other with the drain electrode of M4, the source electrode of M4 connects supply voltage, the grounded-grid of M4, the drain electrode of M5 connect the drain electrode of NMOS pipe M6, the source ground of M6.The grid of M6 links to each other the source ground of M7, the drain electrode output current Ics of M7 with the drain electrode of M6 interconnection and with the grid of M7;

Slope compensation circuit comprises PMOS pipe M8, NMOS pipe M9, capacitor C 1 and bias current Ibias2, the source electrode of M8 connects supply voltage, the grid of M8 links to each other with the grid of M9 and is connected control voltage Vcontrol4, the drain electrode of M8 links to each other with the drain electrode of M9 and an end of capacitor C 1 by bias current Ibias2, as the output voltage signal Vsc of slope compensation circuit, the equal ground connection of the other end of the source electrode of M9, capacitor C 1;

In the PWM modulator, the voltage-to-current comparator comprises NMOS pipe M10～M12, PMOS manages M13～M14, and resistance R 3, R4, the grid of M10 is as an input of PWM modulator, the output Vea that connects error amplifier, the end of the source electrode contact resistance R3 of M10, the other end ground connection of R3, the drain electrode of M10 connects the drain electrode of M13, the source electrode of M13 connects supply voltage, the grid of M13 links to each other with the drain electrode interconnection and with the grid of M14, and the source electrode of M14 connects supply voltage, and the drain electrode of M14 connects the drain electrode of M12, the grid of M12 connect the utmost point and meet bias voltage Vbias1, the source electrode of M12 connects the drain electrode of M11, is connected with the output current Ics of detection current generator in the current detection circuit as another input of PWM modulator, and the grid of M11 is connected with the output voltage signal Vsc of slope compensation circuit as the 3rd input of PWM modulator, the end of the source electrode connecting resistance R4 of M11, the other end ground connection of R4; Amplifying circuit comprises PMOS pipe M15 and NMOS pipe M16, the grid of M15 connects the source electrode of M12 in the voltage-to-current comparator and the drain electrode of M11, the source electrode of M15 connects supply voltage, the drain electrode of M15 connects the drain electrode of M16, and the output as amplifying circuit, the grid of M16 connects bias voltage Vbisa2, the source ground of M16; Shaping circuit comprises inverter INV1, and the input of INV1 connects the output of amplifying circuit, and the output of INV1 is the pulse width modulating signal output.

Advantage of the present invention and remarkable result:

(1) PWM modulator of the present invention is taked voltage-to-current comparator structure, and electric current and the electric current of slope compensation voltage conversion, the electric current sum of current detection circuit output that the EA output end voltage is transformed compare; And behind mirror current source, adopt a N pipe to carry out clamper.This structure has been simplified the pwm circuit structure of traditional complexity greatly, has saved the delay time of loop, has improved the voltage follow ability of system and the response speed of system.

(2) the present invention utilizes two common gate P tube grid voltages to equate this equation relation, obtains simple non-linear current detection architecture.The same with the PWM structure, this simple circuit structure has improved the dynamic electric voltage adjustment capability of system.

(3) slope compensation circuit is implemented in the segmentation slope compensation of uncompensation under the little duty ratio by ramp voltage being converted into electric current stack mode relatively.This structure can be avoided having improved the load capacity of system in the overcompensation situation of duty ratio less than 0.5 time, has expanded system bandwidth, is conducive to improve the voltage follow performance of system.

Description of drawings

Fig. 1 is existing peak electricity flow pattern DC-DC circuit topology block diagram;

Fig. 2 is theory diagram of the present invention;

Fig. 3 is a kind of specific implementation circuit diagram of the present invention.

Embodiment

Such as Fig. 2, the present invention includes PWM modulator, current detection circuit, slope compensation circuit and error amplifier, the PWM modulator receives the signal Vea of slope compensation signal Vsc, current detection signal Ics and error amplifier, carries out calculation process and then obtains the pulse width modulating signal that system needs.Current detection circuit comprises LX voltage transfer circuit 1 and detects electric current I cs=f (I _L) generator 2.LX is the connected node voltage of MP1 pipe and MN1 pipe among Fig. 1, and the output V1 of LX voltage transfer circuit 1 is connected with the input of detection current generator 2; The PWM modulator comprises voltage-to-current comparator 4, amplifying circuit 5 and shaping circuit 6, and slope compensation circuit adopts ramp voltage is converted into electric current stack segmentation slope compensation 3 relatively, and its input signal is control voltage Vcontrol4.The input of voltage-to-current comparator 4 connects respectively the output signal Vsc that detects current generator output current Ics, error amplifier output Vea and slope compensation circuit, the output V2 of voltage-to-current comparator 4 connects the input of amplifying circuit 5, the output V3 of amplifying circuit 5 connects the input of shaping circuit 6, and the output of shaping circuit 6 is the pulse width modulating signal of PWM modulation circuit output.

Such as Fig. 3, in the current detection circuit, LX voltage transfer circuit 1 comprises main switch MP1 and PMOS pipe M1, the source electrode of MP1 connects supply voltage, the grid of MP1 connects control voltage Vcontrol1, and the drain electrode of MP1 is the LX point voltage, connects the source electrode of M1, the grid of M1 meets control signal Vcontrol2, and the drain electrode of M1 is output V1.LX voltage transfer circuit 1 is at the inductive current ascent stage, the voltage on the LX node can be copied and be transferred to Ics=f (IL) generator 2.As shown in Figure 3, adopt a metal-oxide-semiconductor M1 who is operated in dark linear zone, the voltage near-duplicate on the LX point can be come.

Detect current generator 2 and comprise PMOS pipe M2～M5, NMOS pipe M6～M7 and bias current Ibias1, the grid of M2 meets control signal Vcontrol3, the source electrode of M2 connects supply voltage, the source electrode that the drain electrode of M2 connects M3 is connected with the drain electrode output V1 of M1 in the LX voltage transfer circuit 1 as input, the drain electrode of M3 connects bias current Ibias1 and M3, the grid of M5, the other end ground connection of bias current Ibias1, the source electrode of M5 links to each other with the drain electrode of M4, the source electrode of M4 connects supply voltage, the grounded-grid of M4, the drain electrode of M5 connect the drain electrode of NMOS pipe M6, the source ground of M6.The grid of M6 links to each other the source ground of M7, the drain electrode output current Ics of M7 with the drain electrode of M6 interconnection and with the grid of M7.Ics=f (IL) generator 2 can adopt mirror-image structure that the electric current linearity of IL is copied, but because linear structure need to accurately copy electric current, so required circuit structure can be very complicated, the device delay time can be very long.As shown in Figure 3, the present invention adopts a kind of nonlinear organization simple in structure, utilizes metal-oxide-semiconductor M5 to equate this relation with the grid voltage of M7, can obtain Ics and I _LCurrent expression.

Slope compensation circuit 3 comprises PMOS pipe M8, NMOS pipe M9, capacitor C 1 and bias current Ibias2, the source electrode of M8 connects supply voltage, the grid of M8 links to each other with the grid of M9 and is connected control voltage Vcontrol4, the drain electrode of M8 links to each other with the drain electrode of M9 and an end of capacitor C 1 by bias current Ibias2, as the output voltage signal Vsc of slope compensation circuit, the equal ground connection of the other end of the source electrode of M9, capacitor C 1.The input signal Vcontrol4 of slope compensation circuit 3 is the feedback control signal of PWM comparator output terminal signal through producing after the digital circuit.Vcontrol4 is a square-wave signal, and is relevant with system duty cycle, the length of the time that discharges and recharges that can be by control slope compensation electric capacity, thus realize section linear compensating.The compensation slope is 0 when duty ratio is less than 0.5, is a fixing slope compensation slope in duty ratio greater than 0.5 o'clock.

In the PWM modulator, voltage-to-current comparator 4 comprises NMOS pipe M10～M12, PMOS manages M13～M14, and resistance R 3, R4, the grid of M10 is as an input of PWM modulator, the output Vea that connects error amplifier, the end of the source electrode contact resistance R3 of M10, the other end ground connection of R3, the drain electrode of M10 connects the drain electrode of M13, the source electrode of M13 connects supply voltage, the grid of M13 links to each other with the drain electrode interconnection and with the grid of M14, and the source electrode of M14 connects supply voltage, and the drain electrode of M14 connects the drain electrode of M12, the grid of M12 connect the utmost point and meet bias voltage Vbias1, the source electrode of M12 connects the drain electrode of M11, is connected with the output current Ics of detection current generator in the current detection circuit as another input of PWM modulator, and the grid of M11 is connected with the output voltage signal Vsc of slope compensation circuit as the 3rd input of PWM modulator, the end of the source electrode connecting resistance R4 of M11, the other end ground connection of R4.Voltage-to-current comparator 4 is for EA output end voltage Vea, and the output end voltage Vsc of slope compensation circuit 3 changes current signal into, with I _SC, I _CSThe electric current stack is again with I _EAWith I _SC, I _CSAnd compare.Voltage-to-current comparator 4 can adopt a comparator configuration, utilizes the relatively current characteristics of pipe, and input voltage is converted into electric current, directly electric current is compared, and the result that will compare sends into next stage amplifying circuit 5.

Amplifying circuit 5 comprises PMOS pipe M15 and NMOS pipe M16, the grid of M15 connects the source electrode of M12 in the voltage-to-current comparator 4 and the drain electrode output V2 of M11, the source electrode of M15 connects supply voltage, the drain electrode of M15 connects the drain electrode of M16, and the output V3 as amplifying circuit, the grid of M16 connects bias voltage Vbisa2, the source ground of M16..Amplifying circuit 5 can be taked various structures, both can adopt cascodes, also can adopt the common-source stage structure.Under the condition that gain is satisfied, for the circuit structure that obtains to simplify most, Fig. 3 has taked the simplest common-source amplifier structure, and V2 signal input amplifying circuit 5 is obtained signal V3, amplifies and sends into next stage shaping circuit 6.

Shaping circuit 6 comprises inverter INV1, and the input of INV1 connects the output V3 of amplifying circuit, and the output of INV1 is pulse width modulating signal of the present invention.The effect of shaping circuit 6 is for the output signal V3 shaping with amplifying circuit 5.The output signal of amplifying circuit V3 is analog signal, in order to obtain digital signal PWM_OUT at the PWM output, carry out shaping to analog signal.

The operation principle of circuit of the present invention is as follows: when inductive current was in ascent stage, control signal Vcontrol2 made the M1 pipe open work, and control signal Vcontrol1, Vcontrol3 make MP1, M2 manage cut-off.LX voltage transmits by the M1 pipe that is operated in dark linear zone, i.e. V ₁≈ V _LXThe M4 pipe is operated in dark linear zone, is equivalent to a resistance.Bias current Ibias1 provide biasing to M3, and M5 equates that with the grid voltage of M3 M6, M7 are the current mirror duplicate circuit, by regulating the breadth length ratio of M6, M7, can obtain the proportionality coefficient that current mirror copies.Now supposition (W/L) ₇(W/L) ₆=1. utilize M7 to equate V with the grid voltage of M5 _G3=V _G5, can obtain Ics=f (I _L) be shown below:

$\frac{I_L}{u_P{C}_{\mathrm{OX}}{\left(\frac{W}{L}\right)}_{\mathrm{MP}1}[V_{\mathrm{DD}}-V_{\left|\mathrm{TH}\right|\_\mathrm{MP}1}]}=\sqrt{\frac{I_{\mathrm{CS}}}{u_P{C}_{\mathrm{OX}}{\left(\frac{W}{L}\right)}_{M5}}}+V_{\left|\mathrm{TH}\right|\_M5}\frac{I_{\mathrm{CS}}}{2u_P{C}_{\mathrm{OX}}{\left(\frac{W}{L}\right)}_{M4}[V_{\mathrm{DD}}-V_{\left|\mathrm{TH}\right|\_M4}]}-{\mathrm{<figure-callout\; id="3"\; label="V\; SG"\; filenames="HDA00002441873700012.png,HDA00002441873700021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{SG}}$

Wherein, I _LBe inductive current, μ _pBe PMOS pipe transfer rate, C _OXBe PMOS pipe unit are gate oxide electric capacity, (W/L) _MP1And V _{| TH|_MP1}Be respectively breadth length ratio and the threshold voltage of the pipe of PMOS shown in Fig. 1, (W/L) _M4, (W/L) _M5And V _{| TH|_M4}, V _{| TH|_M5}Be respectively breadth length ratio and the threshold voltage of the pipe of M4 among Fig. 3 and M5 pipe, Ics is the drain electrode output current Ics of M7 among Fig. 3, V _DDBe supply voltage.Because bias current I _Bias1Be a constant, so VGS3 is constant in the gate source voltage following formula of M3.Shown in following formula, because be not the principle that adopts current mirror to copy, so the electric current I cs that this current detection circuit obtains and inductive current I _LBe non-linear relation.Sort circuit simple in structure, it is little and low in energy consumption to delay time.

The control signal Vcontrol4 of slope compensation circuit is with the duty ratio relevant feedback control signal of PWM modulator output end signal through producing after the digital circuit, can realize the segmentation slope compensation.When Vcontrol4 is low, M8 opens, and M9 turn-offs, and bias current Ibias2 is to capacitor C 1 charging, output Vsc ramp voltage signal; When Vcontrol4 is high, M8 turn-offs, and M9 opens, and capacitor C 1 is discharged by M9.Smaller when duty, less than 0.5 o'clock, capacitor charging time shortened, and the Vsc voltage of output is less, and deficiency is so that the M11 pipe is opened, and slope compensation voltage cannot be converted to electric current and compare in the PWM modulator.This just means, when duty ratio hour, the slope compensation slope is 0, when duty ratio is larger, is a fixing slope compensation slope, has namely realized the function of section linear compensating.

The PWM modulator is a comparator configuration, and its first order is a current comparator, and the second level is that the one-level amplifier adds shaping circuit.When the PWM modulator was worked, output voltage error amplifier Vea was converted into electric current I by the M10 pipe _Ea, V _ScBe converted into electric current I by the M11 pipe _Sc, M13, M14 are a current mirror, proportionality coefficient is 1, replica current I _Ea, obtain image current I _Ea1Derivation obtains electric current:

$I_{\mathrm{ea}}=V_{\mathrm{ea}}\&times;\frac{g_{m10}}{1+g_{m10}\&times;\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="HDA00002441873700012.png,HDA00002441873700021.png"\; state="\{\{state\}\}">R</figure-callout>}3}$

$I_{\mathrm{SC}}=V_{\mathrm{SC}}\&times;\frac{g_{m11}}{1+g_{m11}\&times;\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="HDA00002441873700012.png"\; state="\{\{state\}\}">R</figure-callout>}4}$

Wherein, g _M10And g _M11Be respectively the mutual conductance of the pipe of M10 among Fig. 3 and M11 pipe, R3 and R4 are the resistance value of resistance shown in Fig. 3.At V2 place, I _EaWith I _SC, I _CSAnd compare, when both had intersection point, V2 place voltage overturn, and passed through amplification, shaping circuit, output signal PWM_OUT.

For guaranteeing that the M14 pipe can copy the electric current of M13 pipe more accurately, the M14 pipe need be operated in the saturation region, has introduced the M12 pipe for this reason.The M12 pipe has the effect of switch and clamper, it is appropriate value that Vbias1 at first is set, next adjusts the M12 pipe makes it be in linear zone when normal operation, so that the Vds of M14 has certain value, make it be operated in the saturation region, and the point voltage of V2 can be too not high, makes M15 be operated in the saturation region and play amplification.

The present invention is different from the PWM modulator structure of the traditional structure of taking a voltage-to-current-voltage+comparator, this voltage-to-current comparator configuration is simplified, and cooperate slope compensation circuit to realize that low duty ratio slope compensation slope is 0 segmentation slope compensation, not only reduced the delay time of system, and the segmentation slope compensation improved system bandwidth, greatly improved the quick dynamic electric voltage adjustment capability of system.

Claims (1)

1. fast transient response pulse width modulation circuit, based on peak electricity flow pattern DC-DC converter topologies, comprise the PWM modulator, current detection circuit, slope compensation circuit and error amplifier, the PWM modulator receives the signal of slope compensation, the signal of current detection signal and error amplifier, carry out calculation process and then obtain the pulse width modulating signal that system needs, it is characterized in that: current detection circuit comprises LX voltage transfer circuit and detects current generator that the output of LX voltage transfer circuit is connected with the input that detects current generator; The PWM modulator comprises voltage-to-current comparator, amplifying circuit and shaping circuit, slope compensation circuit adopts ramp voltage is converted into electric current stack segmentation slope compensation structure relatively, the input of voltage-to-current comparator connects respectively the output signal that detects current generator, error amplifier and slope compensation circuit, the output of voltage-to-current comparator connects the input of amplifying circuit, the output of amplifying circuit connects the input of shaping circuit, the output of shaping circuit is PWM modulation circuit output signal, wherein:

In the current detection circuit, LX voltage transfer circuit comprises switching tube MP1 and PMOS pipe M1, and the source electrode of MP1 connects supply voltage, the grid of MP1 connects control voltage Vcontrol1, the drain electrode of MP1 connects the source electrode of M1, and the grid of M1 meets control signal Vcontrol2, and the drain electrode of M1 is output; Detect current generator and comprise PMOS pipe M2～M5, NMOS pipe M6～M7 and bias current Ibias1, the grid of M2 meets control signal Vcontrol3, the source electrode of M2 connects supply voltage, the drain electrode of M2 connects the source electrode of M3 and the drain electrode of the M1 in the LX voltage transfer circuit, the drain electrode of M3 connects the grid of bias current Ibias1 and M3, M5, the other end ground connection of bias current Ibias1, the source electrode of M5 links to each other with the drain electrode of M4, the source electrode of M4 connects supply voltage, the grounded-grid of M4, the drain electrode of M5 connect the drain electrode of NMOS pipe M6, the source ground of M6.The grid of M6 links to each other the source ground of M7, the drain electrode output current Ics of M7 with the drain electrode of M6 interconnection and with the grid of M7;

Slope compensation circuit comprises PMOS pipe M8, NMOS pipe M9, capacitor C 1 and bias current Ibias2, the source electrode of M8 connects supply voltage, the grid of M8 links to each other with the grid of M9 and is connected control voltage Vcontrol4, the drain electrode of M8 links to each other with the drain electrode of M9 and an end of capacitor C 1 by bias current Ibias2, as the output voltage signal Vsc of slope compensation circuit, the equal ground connection of the other end of the source electrode of M9, capacitor C 1;

In the PWM modulator, the voltage-to-current comparator comprises NMOS pipe M10～M12, PMOS manages M13～M14, and resistance R 3, R4, the grid of M10 is as an input of PWM modulator, the output Vea that connects error amplifier, the end of the source electrode contact resistance R3 of M10, the other end ground connection of R3, the drain electrode of M10 connects the drain electrode of M13, the source electrode of M13 connects supply voltage, the grid of M13 links to each other with the drain electrode interconnection and with the grid of M14, and the source electrode of M14 connects supply voltage, and the drain electrode of M14 connects the drain electrode of M12, the grid of M12 connect the utmost point and meet bias voltage Vbias1, the source electrode of M12 connects the drain electrode of M11, is connected with the output current Ics of detection current generator in the current detection circuit as another input of PWM modulator, and the grid of M11 is connected with the output voltage signal Vsc of slope compensation circuit as the 3rd input of PWM modulator, the end of the source electrode connecting resistance R4 of M11, the other end ground connection of R4; Amplifying circuit comprises PMOS pipe M15 and NMOS pipe M16, the grid of M15 connects the source electrode of M12 in the voltage-to-current comparator and the drain electrode of M11, the source electrode of M15 connects supply voltage, the drain electrode of M15 connects the drain electrode of M16, and the output as amplifying circuit, the grid of M16 connects bias voltage Vbisa2, the source ground of M16; Shaping circuit comprises inverter INV1, and the input of INV1 connects the output of amplifying circuit, and the output of INV1 is the pulse width modulating signal output.

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