CN102832807A - Current control circuit for charge pump - Google Patents

Abstract

The invention discloses a current control circuit for a charge pump, comprising an input voltage detection unit, a self-adaptive control unit and a driving unit, wherein the input end of the input voltage detection unit is connected with an external supply voltage and is used for detecting the external supply voltage; and the input end of the self-adaptive control unit is connected with the output end of an input voltage detection circuit and is used for generating two paths of control signals for controlling a driving circuit; and the driving unit is used for generating an output signal of the current control circuit according to the two paths of control signals generated by the self-adaptive control unit and an inputted external pulse signal. The current control circuit disclosed by the invention regulates the grid-source voltage of a power switch tube self-adaptively according to the inputted supply voltage, when the supply voltage is lower, the grid-source voltage is lower, and the grid-source voltage of the power switch tube cannot be limited; and when the supply voltage is higher, the grid-source voltage of the power switch tube can be automatically limited, and the ripple wave of the input current is further limited.

Description

The current control circuit that is used for charge pump

Technical field

The invention belongs to power technique fields, be specifically related to a kind of design that is applicable to the low overshoot current control circuit of the self adaptation in the charge pump, export to realize stable voltage in order to adjusting to input supply voltage.

Background technology

For electronic system, power supply is various power electronic equipment, and it just looks like the heart of human body; Battery powered mini-plant needs multiple dc voltage usually; Such as; Battery in the beep-pager is 1.5V; And the signal receiving module in the entire equipment, logic module and display screen all need different voltages with different to drive, so must the 1.5V of battery be transformed to multiple different voltage swings to satisfy the disparate modules power demands.In, low current (about＜200mA) application; The charge pump product has advantages such as low noise, low cost and high efficiency than Switching Power Supply, but the power tube grid potential of conventional charge pump is not carried out any restriction, so there is the too big problem of overshoot current in traditional charge pump in transfer process; Impact bigger to supply voltage; Just because of this, need connect big electric capacity at the input supply voltage place of charge pump and carry out filtering, but this can increase the area of pcb board; Damage in order to prevent that surge current from possibly cause electronic system generally all can adopt soft starting circuit to come current limliting simultaneously, but this can make circuit become complicated more undoubtedly.

Summary of the invention

The objective of the invention is to have proposed a kind of current control circuit that is used for charge pump in order to solve excessive problem of the input current overshoot of conventional charge pump when state switches and the complexity that reduces circuit design as much as possible.

Technical scheme of the present invention is: a kind of current control circuit that is used for charge pump comprises: an input voltage detecting unit, a self-adaptive controller and a driver element, wherein,

The input of described input voltage detecting unit links to each other with the supply voltage of outside, is used to detect outside supply voltage;

The input of described self-adaptive controller links to each other with the output of input voltage detection circuit, is used for producing the two path control signal of the said drive circuit of control;

The two path control signal that described driver element produces according to described self-adaptive controller and the external pulse signal of input produce the output signal of said current control circuit.

Further; Described input voltage detecting unit comprises: a PMOS pipe and a bias current sources; The source electrode of described PMOS pipe is as the input of described input voltage detecting unit, and the grid of described PMOS pipe is connected to earth potential with draining to be connected as the output of described input voltage detecting unit and through described bias current sources lotus root.

Further; Described self-adaptive controller comprises: NMOS pipe, the 2nd NMOS pipe, the 3rd NMOS pipe, the 4th NMOS pipe; First bias current sources, second bias current sources and first inverter, second inverter; Wherein, The one NMOS pipe drain electrode is connected to outside supply voltage, and the grid of grid and the 2nd NMOS pipe, the grid of the 3rd NMOS pipe are connected and as the input of described self-adaptive controller, a NMOS manages source electrode and exports the first via control signal of described self-adaptive controller and be connected to earth potential through the first bias current sources lotus root; The second bias current sources the first terminal is connected to outside supply voltage, and second terminal is connected to the drain electrode of the 2nd NMOS pipe, the drain electrode of the 3rd NMOS pipe and the input of first inverter, the source ground of the source electrode of the 2nd NMOS pipe and the 4th NMOS pipe; The source electrode of the 3rd NMOS pipe is connected to the drain electrode of the 4th NMOS pipe; The grid of the 4th NMOS pipe is connected with the output of first inverter, the input of second inverter, and the output of second inverter is exported the second tunnel control signal of described self-adaptive controller.

Further; Described driver element comprises: the 5th NMOS pipe, PMOS pipe, first switch and second switch; Wherein, The grid of the one PMOS pipe is connected with the grid of the 5th NMOS pipe and is used to import outside pulse signal, and the drain electrode of PMOS pipe is connected as the output of described driver element with the drain electrode of the 5th NMOS pipe, and the source electrode of PMOS pipe is connected to outside supply voltage; The source electrode of the 5th NMOS pipe is connected with the first terminal of first switch and the first terminal of second switch; The control terminal of first switch is used for the first via control signal of input adaptive control unit, and the control terminal of second switch is used for the second tunnel control signal of input adaptive control unit, and the second terminal lotus root of second terminal of first switch and second switch is connected to earth potential.

Further, described bias current sources realizes through NMOS pipe that specifically wherein, the drain electrode of described NMOS pipe is as described bias current sources the first terminal, and source electrode is as described bias current sources second terminal, and grid connects outside bias voltage.

Further; Described first switch is specifically realized through PMOS pipe; The grid of described PMOS pipe is as the control terminal of described first switch, and source electrode is as the first terminal of described first switch, and drain electrode is as second terminal of described first switch.

Further; Described second switch is specifically realized through NMOS pipe; The grid of described NMOS pipe is as the control terminal of described second switch, and drain electrode is as the first terminal of described first switch, and source electrode is as second terminal of described first switch.

The invention has the beneficial effects as follows: current control circuit of the present invention can be according to the situation of input supply voltage; Regulate the grid source electric potential of power switch pipe adaptively; When supply voltage is low; The gate source voltage of power switch pipe is less, can not produce excessive input current ripple, the gate source voltage that the circuit that the present invention's this moment proposes can the power-limiting switching tube; When supply voltage is higher; The gate source voltage of power switch pipe is bigger; As not limiting the excessive input current ripple of meeting generation, the gate source voltage of the circuit meeting volitional check power switch pipe that the present invention's this moment proposes is to reach the purpose that limits the input current ripple.Advantages such as control circuit of the present invention has that cost is low, area occupied is little, need not external inductors, high EMI inhibition can be applied in all kinds of charge pumps.

Description of drawings

Fig. 1 is used for the structural representation of the current control circuit of charge pump for the present invention.

Fig. 2 is the structural representation of the input voltage detecting unit among the embodiment.

Fig. 3 is the structural representation of the self-adaptive controller among the embodiment.

Fig. 4 is the structural representation of the control unit among the embodiment.

Fig. 5 is for using the common two times of charge pump construction sketch mapes of current control circuit of the present invention.

Fig. 6 is for adopting two times of charge pump circuit simulation result sketch mapes of circuit of the present invention.

Embodiment

Below in conjunction with accompanying drawing and specific embodiment the present invention is done further explanation.

It is as shown in Figure 1 that the present invention is used for the structural representation of current control circuit of charge pump; Comprise: an input voltage detecting unit, a self-adaptive controller and a driver element, wherein; The input of described input voltage detecting unit links to each other with the supply voltage of outside, is used to detect outside supply voltage V _INThe input of described self-adaptive controller links to each other with the output of input voltage detection circuit, is used for producing the two path control signal V of the said drive circuit of control _C1, V _C2The two path control signal V that described driver element produces according to described self-adaptive controller _C1, V _C2And the external pulse signal of input

Produce the output signal of said current control circuit

In the such scheme, a kind of implementation of input voltage detecting unit is as shown in Figure 2, comprising: a PMOS pipe MP0 and a bias current sources I _B, the source electrode of MP0 is as the input of described input voltage detecting unit, and the grid of MP0 is connected as the output of input voltage detecting unit and through bias current sources I with drain electrode _BLotus root is connected to earth potential.

In the such scheme, a kind of implementation of self-adaptive controller is as shown in Figure 3, comprising: NMOS pipe MN10, the 2nd NMOS pipe MN11, the 3rd NMOS pipe MN12, the 4th NMOS manage MN13, the first bias current sources k ₁I _B, the second bias current sources k ₂I _BWith the first inverter INV1, the second inverter INV2; Wherein, The MN10 drain electrode is connected to outside supply voltage; The grid of grid and MN11, the grid of MN12 are connected and as the input of described self-adaptive controller, the MN10 source electrode is exported the first via control signal V of described self-adaptive controller _C1And through the first bias current sources k ₁I _BLotus root is connected to earth potential; The second bias current sources k ₂I _BThe first terminal is connected to outside supply voltage V _IN, second terminal is connected to the drain electrode of MN11, the drain electrode of MN12 and the input of the first inverter INV1, the source electrode of MN11 and the source ground of MN13; The source electrode of MN12 is connected to the drain electrode of MN13, and the grid of MN13 is connected with the output of the first inverter INV1, the input of the second inverter INV2, and the output of the second inverter INV2 is exported the second tunnel control signal V of described self-adaptive controller _C2

In the such scheme; A kind of implementation of driver element is as shown in Figure 4; Comprise: the 5th NMOS pipe MN14, a PMOS manage MP1, first K switch 1 and second switch K2, and wherein, the grid of PMOS pipe MP1 is connected with the grid of MN14 and is used to import outside pulse signal The drain electrode of MP1 is connected with the drain electrode of MN14 as the output signal of the output output current control circuit of described driver element

The source electrode of MP1 is connected to outside supply voltage V _IN, the source electrode of MN14 is connected with the first terminal of the first terminal of K1 and K2, and the control terminal of K1 is used for the first via control signal V of input adaptive control unit _C1, the control terminal of K2 is used for the second tunnel control signal V of input adaptive control unit _C2, the second terminal lotus root of second terminal of K1 and second switch is connected to earth potential.Work as V _INIt is less when not needing current limliting,

With

It is simple anti-phase relation; Work as V _INIt is bigger when needing current limliting, Will be restricted analog level, specifically can be referring to following analysis.

In Fig. 4, first K switch 1 specifically realizes through PMOS pipe and NMOS pipe with second switch K2, and is concrete; K1 realizes through PMOS pipe MP2; The grid of described MP2 is as the control terminal of K1, and source electrode is as the first terminal of K1, and drain electrode is as second terminal of K1; K2 realizes that through a NMOS pipe MN15 grid of MN15 is as the control terminal of K2, and drain electrode is as the first terminal of described K2, and source electrode is as second terminal of described K2.

Here, bias current sources I _B, k ₁I _B, k ₂I _BCan realize that all wherein, the drain electrode of NMOS pipe is as the bias current sources the first terminal through NMOS pipe, source electrode is as bias current sources second terminal, and grid connects outside bias voltage.Here just in order to express easily use k ₁, k ₂Explain the relation of three bias current source sizes, its concrete size can be chosen according to actual conditions.

Provide the operation principle of circuit proposed by the invention below.

As shown in Figure 2, by the PMOS pipe MP0 and a current source I of diode connected mode _BForm and be used for detecting V _INThe size of input voltage, whether complete opening perhaps carries out current limliting to judge power tube to late-class circuit then.In the circuit power up, if V _INWhen above than the high twice overdrive voltage of threshold voltage of MP0 pipe, biasing circuit and operate as normal, MP0 can be operated in the saturation region so, has following relation to satisfy:

$I_B=I_{\mathrm{MP}0}=\frac{1}{2}{K}_P{\left(\frac{W}{L}\right)}_{\mathrm{MP}0}{(V_{\mathrm{IN}}-V_{\mathrm{DET}}-|V_{\mathrm{THP}}\left|\right)}^2---\left(1\right)$

V in the formula (1) _THPThreshold voltage, V for MP0 _DETBe the output voltage that input supply voltage detects, COEFFICIENT K _P=μ _pC _Ox, μ _pCarrier mobility for the PMOS pipe can solve V through following formula _DET, promptly

$V_{\mathrm{DET}}=V_{\mathrm{IN}}-\left|V_{\mathrm{THP}}\right|-\sqrt{\frac{{2I}_B}{K_P{(W/L)}_{\mathrm{MP}0}}}---\left(1\right)$

From formula (2), can find out, at current source current I _BSize and MP0 breadth length ratio (W/L) _MP0Under certain situation, V _DETWith input supply voltage V _INTherefore linear variation passes through V _DETJust can know V _INSize, just can offer the situation that back level adaptation control unit comes decision circuitry.

As shown in Figure 3, the core of self-adaptive controller mainly is made up of two parts, and a part is by MN10 and current source k ₁I _BConstitute level shift, be used for producing first via control signal V _C1Another part is managed MN11, MN12, MN13 by NMOS, inverter INV1, INV2 and current source k ₂I _BConstitute adaptive control judgement and hysteresis circuitry, be used for producing the second tunnel control signal V _C2The major function of this unit is the detection voltage V according to front stage circuits output _DETSpecifically judge whether power tube needs current limliting.

When the prime output voltage V _DETSmaller, on the one hand, NMOS pipe MN10 ends output voltage V _C1Can be low always; The MN11 pipe also can end on the other hand, node voltage V _INV1Keep high potential always, after inverter INV1 effect, node voltage V _INV2Keep electronegative potential, final output voltage V always _C2Be high always.When the prime output voltage V _DETEnough big, on the one hand, NMOS pipe MN10 meeting conducting, output voltage V _C1Can be by the low V that becomes _DET-V _GS10, V wherein _GS10Gate source voltage for MN10; The MN11 pipe also can conducting on the other hand, node voltage V _INV1Become electronegative potential, after inverter INV1 effect, node voltage V _INV2Become high potential, and pass through the effect of the positive feedback of MN13, MN12 and INV1 formation, V _INV2It is faster that the hopping edge will become, final output voltage V _C2Be low always, V _DETExist and trigger amount of hysteresis, mainly realize by MN13, M12 and INV1.

Provide concrete quantitative analysis below.

Work as V _DETEnough big, make the electric current of MN11 be equal to the electric current k of current source ₂I _BThe time, node voltage V _INV1Can descend, inverter INV1 begins turning, and MN13 also is initially located in conducting state soon, and following formula is arranged this moment:

$k_2{I}_B=I_{\mathrm{MN}11}=\frac{1}{2}{K}_N{\left(\frac{W}{L}\right)}_{\mathrm{MN}11}{(V_{\mathrm{DET}}-V_{\mathrm{THN}})}^2---\left(2\right)$

Wherein, K _N=μ _nC _Ox, μ _nBe the carrier mobility of NMOS pipe, C _OxFor unit are grid oxygen electric capacity, can solve through top formula (3) Can get the threshold voltage V that circuit begins turning in substitution (2) formula _INHFor:

$V_{\mathrm{INH}}=V_{\mathrm{THP}}+\sqrt{\frac{2I_B}{K_P{(W/L)}_{\mathrm{MP}0}}}{+V}_{\mathrm{THN}}+\sqrt{\frac{2k_2{I}_B}{K_N{(W/L)}_{\mathrm{MN}11}}}---\left(3\right)$

Work as V _DETWhen bigger, node voltage V _INV1Can descend enough lowly, can make V _INV2Upset is high level, and this moment, the M14 pipe can be regarded switching tube as, because be operated in dark linear zone, the electric current sum that then flows through MN11 and MN12 equals tail current source k ₂I _BSize, according to electric current Kirchhoff's law, k ₂I _B=I _MN11+ I _MN12, and think that MN11 and MN12 are operated in the saturation region, that is:

$k_2{I}_B=I_{\mathrm{MN}11}+I_{\mathrm{MN}12}=\frac{1}{2}{K}_N{\left(\frac{W}{L}\right)}_{\mathrm{MN}11}{(V_{\mathrm{DET}}-V_{\mathrm{THN}})}^2+\frac{1}{2}{K}_N{\left(\frac{W}{L}\right)}_{\mathrm{MN}12}{(V_{\mathrm{DET}}-V_{\mathrm{THN}})}^2---\left(4\right)$

Can solve through top formula (5) The substitution formula can get in (2), the threshold voltage V that circuit begins turning _INLFor:

$V_{\mathrm{INL}}=\left|V_{\mathrm{THP}}\right|+\sqrt{\frac{2I_B}{K_P{(W/L)}_{\mathrm{MP}0}}}+V_{\mathrm{THN}}+\sqrt{\frac{2k_2{I}_B}{K_N[{(W/L)}_{\mathrm{MN}11}+{(W/L)}_{\mathrm{MN}12}]}}---\left(5\right)$

MN10 and k ₁I _BConstitute level shift circuit, because of output voltage V _C1Can obtain according to following formula (7), establish MN10 and be operated in the saturation region, have:

$I_B=I_{\mathrm{MN}10}=\frac{1}{2}{K}_N{\left(\frac{W}{L}\right)}_{\mathrm{MN}10}{(V_{\mathrm{DET}}-V_{C1}-V_{\mathrm{THN}})}^2---\left(6\right)$

Have through finding the solution top equality; In

substitution formula (2), can get:

${\mathrm{<figure-callout\; id="1"\; label="V\; C"\; filenames="HDA00002081346900022.png"\; state="\{\{state\}\}">V</figure-callout>}}_C=V_{\mathrm{IN}}-\left|V_{\mathrm{THP}}\right|-\sqrt{\frac{2I_B}{K_P{(W/L)}_{\mathrm{MP}0}}}-V_{\mathrm{THN}}-\sqrt{\frac{2I_B}{K_N{(W/L)}_{\mathrm{MN}10}}}---\left(7\right)$

In a word, can know according to formula (4), (6) and (8), when input supply voltage less than V _INHThe time, adaptation control circuit can be to power tube grid current limliting, and this moment, the driving force of power tube did not receive any restriction; When input supply voltage greater than V _INHThe time, adaptation control circuit just can begin the power tube grid is begun current limliting, and this threshold voltage size specifically can be through design (W/L) _MP0, (W/L) _MN11, k ₂And I _BSatisfy the actual conditions requirement.In case after decision circuitry thought that power tube needs current limliting, the electric current that power tube flows through began to be subject to V _C1The control of level, this level specifically can be through designs (W/L) _MP0, (W/L) _MN10And I _BSatisfy the actual conditions requirement; When input supply voltage reduces and less than V gradually _INLThe time, adaptation control circuit can this shows that the amount of hysteresis of state handover trigger level is V from the power tube limited current state being switched to not limited current state, reach the purpose that does not influence the power tube driving force _HYS, i.e. V _HYS=V _INH-V _INL, so:

$V_{\mathrm{HYS}}=\sqrt{\frac{2k_2{I}_B}{K_N{(W/L)}_{\mathrm{MN}11}}}-\sqrt{\frac{2k_2{I}_B}{K_N[{(W/L)}_{\mathrm{MN}11}+{(W/L)}_{\mathrm{MN}12}]}}---\left(8\right)$

Can be according to top formula (9) through design (W/L) _MN11(W/L) _MN12Size obtains suitable hysteresis voltage amount, misses the phenomenon of overturning to prevent state, and then influences the operate as normal of circuit.

As shown in Figure 4; The transmission gate that driver element is made up of MP1, MN14; And current limliting metal-oxide-semiconductor MN15, MP2 constitute, and output voltage is

gate control signal as power tube.

When grid-control digital signal when being low level; PMOS pipe MP1 opens; Output voltage this moment

is a high level, and this can let power tube be in the shutoff cycle.

When grid-control digital signal

when being high level; NMOS pipe MN14 opens; This moment, the power tube grid potential was mainly decided by the conducting situation of MN15 and MP2, played the effect of restriction overshoot current.

The circuit working process is divided two kinds of situation.First kind of situation: input voltage V _INLower, V _C2Be output as high level, V _C1Be low level, so node voltage V _SBe approximately ground level (conduction voltage drop of ignoring MN15), this moment need be to the power tube gate-voltage limit, if the gate voltage of power tube is limited the driving force that can reduce power tube on the contrary; Second kind of situation: input voltage V _INGreater than V _INHThe time, V _C2Output hopping is a low level, and MN15 turn-offs, and the power tube grid voltage can be subject to MP2, like this above the power tube to overcharge electric current just not too large.

In order to verify the performance of circuit proposed by the invention, be example with the common two times of charge pumps that embed circuit of the present invention here, provide the actual effect of circuit of the present invention through emulation.Common two times of charge pump integrated circuits generally are made up of power switch pipe, comparator, control circuit, and are as shown in Figure 5.The simulation result of circuit is as shown in Figure 6, can find out at 25 ℃ of temperature, V _IN=5V, clock frequency are under the 2.2Mhz condition, and the overshoot current of charge pump when state exchange reduces greatly.When this circuit structure is applied in the effect that reduces overshoot current is arranged really in the charge pump circuit through tables of simulation results is clear, and effect is remarkable.

Control circuit of the present invention can be applicable to any reduction charge pump that needs and imports in the design of overshoot current; Through adopting the technology that limits the power tube grid potential; Can guarantee conventional charge pump low quiescent current and need not under the situation of external inductors, reduce the input overshoot current size of charge pump when different conditions switches greatly.

Those of ordinary skill in the art will appreciate that embodiment described here is in order to help reader understanding's principle of the present invention, should to be understood that protection scope of the present invention is not limited to such special statement and embodiment.Those of ordinary skill in the art can make various other various concrete distortion and combinations that do not break away from essence of the present invention according to these teachings disclosed by the invention, and these distortion and combination are still in protection scope of the present invention.

Claims (7)

1. current control circuit that is used for charge pump comprises: an input voltage detecting unit, a self-adaptive controller and a driver element, wherein,

The input of described input voltage detecting unit links to each other with the supply voltage of outside, is used to detect outside supply voltage;

The input of described self-adaptive controller links to each other with the output of input voltage detection circuit, is used for producing the two path control signal of the said drive circuit of control;

The two path control signal that described driver element produces according to described self-adaptive controller and the external pulse signal of input produce the output signal of said current control circuit.

2. current control circuit according to claim 1; It is characterized in that; Described input voltage detecting unit comprises: a PMOS pipe and a bias current sources; The source electrode of described PMOS pipe is as the input of described input voltage detecting unit, and the grid of described PMOS pipe is connected to earth potential with draining to be connected as the output of described input voltage detecting unit and through described bias current sources lotus root.

3. current control circuit according to claim 1 and 2; It is characterized in that; Described self-adaptive controller comprises: NMOS pipe, the 2nd NMOS pipe, the 3rd NMOS pipe, the 4th NMOS pipe; First bias current sources, second bias current sources and first inverter, second inverter, wherein, the drain electrode of NMOS pipe is connected to outside supply voltage; The grid of the grid of grid and the 2nd NMOS pipe, the 3rd NMOS pipe is connected and as the input of described self-adaptive controller, NMOS pipe source electrode is exported the first via control signal of described self-adaptive controller and is connected to earth potential through the first bias current sources lotus root; The second bias current sources the first terminal is connected to outside supply voltage, and second terminal is connected to the drain electrode of the 2nd NMOS pipe, the drain electrode of the 3rd NMOS pipe and the input of first inverter, the source ground of the source electrode of the 2nd NMOS pipe and the 4th NMOS pipe; The source electrode of the 3rd NMOS pipe is connected to the drain electrode of the 4th NMOS pipe; The grid of the 4th NMOS pipe is connected with the output of first inverter, the input of second inverter, and the output of second inverter is exported the second tunnel control signal of described self-adaptive controller.

4. according to claim 1 or 2 or 3 described current control circuits; It is characterized in that; Described driver element comprises: the 5th NMOS pipe, PMOS pipe, first switch and second switch; Wherein, The grid of the one PMOS pipe is connected with the grid of the 5th NMOS pipe and is used to import outside pulse signal, and the drain electrode of PMOS pipe is connected as the output of described driver element with the drain electrode of the 5th NMOS pipe, and the source electrode of PMOS pipe is connected to outside supply voltage; The source electrode of the 5th NMOS pipe is connected with the first terminal of first switch and the first terminal of second switch; The control terminal of first switch is used for the first via control signal of input adaptive control unit, and the control terminal of second switch is used for the second tunnel control signal of input adaptive control unit, and the second terminal lotus root of second terminal of first switch and second switch is connected to earth potential.

5. current control circuit according to claim 4; It is characterized in that; Described bias current sources realizes through NMOS pipe that specifically wherein, the drain electrode of described NMOS pipe is as described bias current sources the first terminal; Source electrode is as described bias current sources second terminal, and grid connects outside bias voltage.

6. current control circuit according to claim 4; It is characterized in that; Described first switch is specifically realized through PMOS pipe; The grid of described PMOS pipe is as the control terminal of described first switch, and source electrode is as the first terminal of described first switch, and drain electrode is as second terminal of described first switch.

7. according to claim 4 or 6 described current control circuits; It is characterized in that; Described second switch is specifically realized through NMOS pipe; The grid of described NMOS pipe is as the control terminal of described second switch, and drain electrode is as the first terminal of described first switch, and source electrode is as second terminal of described first switch.

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