GB2312576A - Increasing switching speed of bipolar circuit for charge pump by clamping transistors to prevent saturation - Google Patents

Increasing switching speed of bipolar circuit for charge pump by clamping transistors to prevent saturation Download PDF

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Publication number
GB2312576A
GB2312576A GB9608616A GB9608616A GB2312576A GB 2312576 A GB2312576 A GB 2312576A GB 9608616 A GB9608616 A GB 9608616A GB 9608616 A GB9608616 A GB 9608616A GB 2312576 A GB2312576 A GB 2312576A
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GB
United Kingdom
Prior art keywords
bipolar switch
bipolar
current
clamping
transistor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB9608616A
Other versions
GB2312576B (en
GB9608616D0 (en
Inventor
Thien Huynh-Luong
Heinz Lehning
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Motorola Solutions Inc
Original Assignee
Motorola Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc filed Critical Motorola Inc
Priority to GB9608616A priority Critical patent/GB2312576B/en
Publication of GB9608616D0 publication Critical patent/GB9608616D0/en
Publication of GB2312576A publication Critical patent/GB2312576A/en
Priority to HK98102810A priority patent/HK1003686A1/en
Application granted granted Critical
Publication of GB2312576B publication Critical patent/GB2312576B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/51—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used
    • H03K17/56—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices
    • H03K17/60—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors
    • H03K17/615—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the components used by the use, as active elements, of semiconductor devices the devices being bipolar transistors in a Darlington configuration
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/06—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider
    • H02M3/07—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps
    • H02M3/073—Charge pumps of the Schenkel-type
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/04—Modifications for accelerating switching
    • H03K17/042—Modifications for accelerating switching by feedback from the output circuit to the control circuit
    • H03K17/0422—Anti-saturation measures

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Electronic Switches (AREA)

Abstract

A bipolar switch arrangement (100) for coupling to a switched capacitor has a switched node (110) and first (122) and second (160) bipolar switches coupled to switch the node (110) between a first and a second voltage. A voltage-current converter (140) is coupled to control the first and second bipolar switches (122,160) such that they are in antiphase. First and second clamping networks (120,130) are coupled between the first and second switches (122, 160) respectively and the voltage-current converter (140). In this way the first and second clamping networks (120,130) are arranged for clamping the first and second bipolar switches (122, 160) respectively, thus preventing saturation and improving current regulation of the arrangement (100).

Description

BIPOLAR SWITCH ARRANGEMENT Field of the Invention This invention relates to bipolar switch arrangements and particularly but not exclusively to bipolar switch arrangements for driving charge pumps.
Background of the Invention Integrated charge pump circuits are very common in MOS (Metal Oxide Semiconductor) technology, for example to generate the programming voltage of EEPROMs (Electrically erasable read-only-memories). MOS technology is ideal for this because of the low voltage drop and low current consumption of the MOS devices.
Charge pumps formed in bipolar technology, are based either on a PNP mirror current or PNP base current control arrangement, for providing current to charge storage and parasitic capacitors. In both cases, PNP transistors go into saturation and limit the switching frequency. Moreover the current required to drive the PNP transistors is significantly higher than that required for a MOS device, as is current consumption.
This invention seeks to provide a bipolar switch which mitigates the above mentioned disadvantages.
Summarv of the Invention According to the present invention there is provided a bipolar switch arrangement, comprising a switched node for coupling to a switched capacitor; first and second bipolar switches coupled to switch the node between a first and a second voltage; a voltage-current converter coupled to control the first and second bipolar switches such that they are in antiphase; and, first and second clamping networks coupled between the first and second switches respectively and the voltage-current converter, wherein the first and second clamping networks are arranged for clamping the first and second bipolar switches respectively, thus preventing saturation and improving current regulation thereof.
Preferably the first clamping network comprises a driving transistor and two clamping schottky diodes. The first bipolar switch and the driving transistor of the first clamping network are preferably arranged as a Darlington transistor device.
Preferably the two clamping schottky diodes are arranged to compensate base-emitter voltage drops of the Darlington transistor device to prevent saturation thereof, and to deviate current to the first bipolar switch thus providing low steady state current consumption. The second clamping network preferably comprises a clamping transistor arranged to prevent saturation of the second bipolar switch.
Preferably the voltage current converter circuit comprises a first current source transistor, arranged for providing current control to the first bipolar switch via the first clamping network, and a second current source transistor, arranged for providing current control to the second bipolar switch via the second clamping network. The voltage current converter circuit preferably further comprises a voltage-to -current converting resistor. Preferably the first bipolar switch is a PNP transistor and the second bipolar switch is a schottky NPN transistor.
In this way saturation is avoided and current regulation is significantly improved, providing an efficient and fast bipolar switch arrangement.
Brief Description of the Drawing(s) An exemplary embodiment of the invention will now be described with reference to the drawings in which: FIG. 1 shows a prior art charge pump circuit.
FIG.2 shows a graph of voltage/time characteristics of the prior art charge pump circuit of FIG.1.
FIG.3 shows a preferred embodiment of a bipolar switch arrangement in accordance with the invention.
Detailed Descnplaon of a Preferred Embodiment Referring to FIG. 1, there is shown a prior art charge pump circuit 5. The charge pump circuit 5 has four charge stages 10, 20, 30 and 40. Each charge stage has a switch (12, 22, 32 and 42), a capacitor (15, 25, 35 and 45) and a diode (17, 27, 37 and 47). Each charge stage 10, 20, 30 and 40 also has an input and an output.
With reference to the first charge stage 10, the diode 17 is coupled between the input and the output. Also coupled to the output is one terminal of the capacitor 15. The other terminal of the capacitor 15 is coupled to the switch 12, which is arranged for switching this terminal between a supply voltage Vcc and ground. The other charge stages 20, 30 and 40 are arranged similarly.
The input of the first charge stage 10 is also coupled to the supply voltage Vcc. The output of the first stage 10 is coupled to the input of the second stage 20, and so on. The output of the fourth stage 40 is coupled to a final diode 57, a smoothing capacitor 55, and to a load 50.
In operation, the switches 12 and 32 are switched together, in antiphase with switches 22 and 42. In this way charge accumulates in successive capacitors from left to right. Capacitor 15 stores Q of charge (where Q=C.Vcc), capacitor 25 stores 2Q of charge, and so on.
Referring now also to FIG.2, there is shown a timing diagram of diode cathode voltages of the charge pump circuit 5. The diode voltage drop is VD and the ripple produced by the load is VC. Charge stages 10 and 30 are switched on together during a first period 60 and a third period 80 to accumulate the charge while charge stages 20 and 40 transfer the charge.
Likewise, charge stages 20 and 40 are switched on together during a second period 70 and a fourth period 90. The line 95 represents the output voltage across the load 50. Ideally this would be steady DC voltage, but is in practice subject to ripples imposed by the capacitors.
Referring now also to FIG.3, there is shown a bipolar charge pump switch arrangement 100 in accordance with a preferred embodiment of the invention, including a switched node 110, arranged for coupling to a switched capacitor such as capacitor 15 of FIG. 1.
A first switching network 120 is coupled to the switched node 110, and comprises a supply voltage (Vcc) input 121, a driving transistor 126 having collector, emitter and base electrodes, first and second schottky diodes 124 and 125, and first and second resistors 123 and 127.
A first bipolar switch 122, preferably a PNP transistor, having collector, emitter and base electrodes is coupled via the emitter electrode to the supply voltage input 121 and via the collector electrode to the switched node 110.
The base electrode of the first bipolar switch 122 is coupled via the first resistor 123 to the supply voltage input 121. The first and second schottky diodes 124, 125 are arranged in series, and are coupled between the collector electrode of the first bipolar switch 122 and the base electrode of the driving transistor 126, which is a preferably a substrate PNP transistor having a high current gain. The base electrode of the driving transistor 126 is also coupled via the second resistor 127 to the supply voltage input 121 and to a current terminal 128 to be further described below. The emitter electrode of the driving transistor 126 is coupled to the base electrode of the first bipolar switch 122. The collector electrode of the driving transistor 126 is coupled to ground. In this way a high current gain Darlington transistor arrangement is formed, having a base electrode effectively controlled by the current terminal 128, and not requiring a large driver current.
A second switching network 130 comprises a transistor 135, preferably an NPN bipolar transistor, having collector, emitter and base electrodes, and a resistor 137. The base electrode of the transistor 135 is coupled to a reference voltage input (Vref) 132. The collector electrode is coupled to the supply voltage input 121 of the first switching network, and the emitter electrode is coupled via the resistor 137 to the supply voltage input 121, forming an emitter-follower arrangement.
A voltage-current converter circuit 140 comprises first and second current source transistors 142 and 144, each with collector, emitter and base electrodes. The base electrodes of the first and second current source transistors 142 and 144 are both coupled to a command voltage input 145.
The emitter electrodes of the first and second current source transistors 142 and 144 are both coupled to ground via a resistor 146. The collector electrode of the first current source transistor 142 is coupled to the current terminal 128 of the first switching network 120. The collector electrode of the second current source transistor 144 is coupled to the emitter electrode of transistor 135 of the second switching network 130.
A schottky diode 150 is coupled between the emitter electrode of transistor 135 of the second switching network 130, and the switched node 110.
Similarly a second bipolar switch 160, preferably an NPN transistor, has a base electrode coupled to the emitter electrode of transistor 135, a collector electrode coupled to the switched node 110, and an emitter electrode coupled to ground. In this way the base electrode of the second bipolar switch 160 is controlled by the second current source transistor 144.
In operation, the switched node 110 is to be repeatedly switched between Vcc and ground. The second bipolar switch 160 selectively couples the switched node 110 to ground. The schottky diode 150 is used to clamp the collector electrode of the second bipolar switch 160 and substantially prevent saturation thereof. The first bipolar switch 122 selectively couples the switched node 110 to the supply voltage input 121.
The voltage-current converter circuit 140 receives a command voltage at the command voltage input 145, which is essentially the switching clock phase.
During an on-phase, the first and second current source transistors 142, 144 are switched on. The collector of the first current source transistor 142 supplies the current to the current terminal 128 of the first switching network 120, thus turning on the driving transistor 126 and the first bipolar switch 122. The collector electrode of the second current source transistor 144 provides current to the emitter electrode of the transistor 135 of the second switching network 130, thus turning it on and turning off the second bipolar switch 160.
During an off-phase, the first and second current source transistors 142, 144 are switched off, thus isolating the current terminal 128 and the emitter electrode of transistor 135.
The first switching network 120 is driven by the first current source transistor 142. While a weak current is supplied by the first current source transistor 142 to the base of the driving transistor 126, by the virtue of the Darlington arrangement of the driving transistor 126 and the first bipolar switch 122 a strong current flows from the collector of the first bipolar switch 122 therethrough to the switched node 110. The voltage at the switched node 110 increases rapidly until it reaches (Vcc - 2.Vbe + 2.Vd), where Vbe is the base-emitter voltages of the first bipolar switch 122 and the driving transistor 126 and Vd is the diode voltage of the first and second schottky diodes 124 and 125.
At this point the first and second schottky diodes 124 and 125 begin to conduct and the current of the first current source transistor 142 is deviated through the first and second schottky diodes 124 and 125 into the collector electrode of the first bipolar switch 122. This ensures that the first bipolar switch 122 does not saturate, and reduces the steady state current consumption.
When the first current source transistor 142 is turned off, the first resistor 123 is employed to aid the discharge of collector-base capacitance of the first bipolar switch 122, thus increasing turn-off speed and assure a clean 'offstate' of the first bipolar switch 122. Similarly, the second resistor 127 absorbs the leakage current from the first current source transistor 142 to assure a clean 'off-state' of the entire Darlington arrangement.
The second switching network 130 is driven by the second current source transistor 144, and is employed to aid the switching of the second bipolar switch 160 without saturating the second current source transistor 144.
This is achieved with the emitter-follower arrangement of transistor 135.
The emitter electrode of transistor 135 absorbs current surplus from the second current source transistor 144, clamping the collector electrode thereof substantially to Vref, the value of the reference voltage input 132.
Specifically the voltage is clamped to Vref-Vbe, where Vbe is the base emitter voltage of transistor 135.
When the second current source transistor 144 is turned off, resistor 137 conveys current from the supply voltage input 121 to the base electrode of the second bipolar switch 160, turning it on. The value of resistor 137 is chosen such that the second bipolar switch 160 is only turned on after the first bipolar switch 122 is switched off, thus avoiding current circulation between first and second bipolar switches 122 and 160 respectively and therefore reducing current consumption.
It will be appreciated by a person skilled in the art that alternative embodiments to the one described above are possible. For example, alternative arrangements of transistors and resistors which achieve substantially the same function as described above are envisaged.
Furthermore a number of Darlington arrangements with corresponding schottky diodes could be used to augment the single arrangement described above.

Claims (9)

Claims
1. A bipolar switch arrangement, comprising: a switched node for coupling to a switched capacitor; first and second bipolar switches coupled to switch the node between a first and a second voltage; a voltage-current converter coupled to control the first and second bipolar switches such that they are in antiphase; and, first and second clamping networks coupled between the first and second switches respectively and the voltage-current converter, wherein the first and second clamping networks are arranged for clamping the first and second bipolar switches respectively, thus preventing saturation and improving current regulation thereof.
2. The bipolar switch arrangement as claimed in claim 1 wherein the first clamping network comprises a driving transistor and two clamping schottky diodes.
3. The bipolar switch arrangement as claimed in claim 2 wherein the first bipolar switch and the driving transistor of the first clamping network are arranged as a Darlington transistor device.
4. The bipolar switch arrangement as claimed in claim 3 wherein the two clamping schottky diodes are arranged to compensate base-emitter voltage drops of the Darlington transistor device to prevent saturation thereof, and to deviate current to the first bipolar switch thus providing low steady state current consumption.
5. The bipolar switch arrangement as claimed in any preceding claim wherein the second clamping network comprises a clamping transistor arranged to prevent saturation of the second bipolar switch.
6. The bipolar switch arrangement as claimed in any preceding claim wherein the voltage current converter circuit comprises a first current source transistor, arranged for providing current control to the first bipolar switch via the first clamping network, and a second current source transistor, arranged for providing current control to the second bipolar switch via the second clamping network.
7. The bipolar switch arrangement as claimed in any preceding claim wherein the voltage current converter circuit further comprises a voltage-to -current converting resistor.
8. The bipolar switch arrangement as claimed in any preceding claim wherein the first bipolar switch is a PNP transistor and the second bipolar switch is a schottky NPN transistor.
9. A bipolar switch arrangement substantially as hereinbefore described and with reference to FIG.3 of the drawings.
GB9608616A 1996-04-24 1996-04-24 Bipolar switch arrangement Expired - Fee Related GB2312576B (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB9608616A GB2312576B (en) 1996-04-24 1996-04-24 Bipolar switch arrangement
HK98102810A HK1003686A1 (en) 1996-04-24 1998-04-02 Bipolar switch arrangement

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9608616A GB2312576B (en) 1996-04-24 1996-04-24 Bipolar switch arrangement

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Publication Number Publication Date
GB9608616D0 GB9608616D0 (en) 1996-07-03
GB2312576A true GB2312576A (en) 1997-10-29
GB2312576B GB2312576B (en) 2000-06-07

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HK (1) HK1003686A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10045693A1 (en) * 2000-09-15 2002-04-04 Infineon Technologies Ag Charge pump circuit
EP1035651A3 (en) * 1999-03-08 2003-11-05 Texas Instruments Incorporated A driving circuit

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3970871A (en) * 1974-02-19 1976-07-20 Gte Automatic Electric Laboratories Incorporated Negative DC to positive DC converter
EP0608151A2 (en) * 1993-01-21 1994-07-27 Gennum Corporation A high speed and low drift charge pump circuit

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3970871A (en) * 1974-02-19 1976-07-20 Gte Automatic Electric Laboratories Incorporated Negative DC to positive DC converter
EP0608151A2 (en) * 1993-01-21 1994-07-27 Gennum Corporation A high speed and low drift charge pump circuit

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1035651A3 (en) * 1999-03-08 2003-11-05 Texas Instruments Incorporated A driving circuit
DE10045693A1 (en) * 2000-09-15 2002-04-04 Infineon Technologies Ag Charge pump circuit
US6850111B1 (en) 2000-09-15 2005-02-01 Infineon Technologies Ag Charge pump circuit

Also Published As

Publication number Publication date
GB2312576B (en) 2000-06-07
HK1003686A1 (en) 1998-11-06
GB9608616D0 (en) 1996-07-03

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PCNP Patent ceased through non-payment of renewal fee

Effective date: 20020424