EP1119908A1 - Electronic circuit for imitating a capacitor with variable capacitance - Google Patents

Electronic circuit for imitating a capacitor with variable capacitance

Info

Publication number
EP1119908A1
EP1119908A1 EP00956297A EP00956297A EP1119908A1 EP 1119908 A1 EP1119908 A1 EP 1119908A1 EP 00956297 A EP00956297 A EP 00956297A EP 00956297 A EP00956297 A EP 00956297A EP 1119908 A1 EP1119908 A1 EP 1119908A1
Authority
EP
European Patent Office
Prior art keywords
electronic circuit
separate
inputs
voltages
ofthe
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.)
Withdrawn
Application number
EP00956297A
Other languages
German (de)
French (fr)
Inventor
Franciscus M. L. Van Der Goes
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.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
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 Koninklijke Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Priority to EP00956297A priority Critical patent/EP1119908A1/en
Publication of EP1119908A1 publication Critical patent/EP1119908A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
    • G11C11/24—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using capacitors
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H11/00—Networks using active elements
    • H03H11/46—One-port networks
    • H03H11/48—One-port networks simulating reactances
    • H03H11/481—Simulating capacitances

Definitions

  • the invention relates to an electronic circuit for imitating a capacitor with variable capacitance.
  • Such an electronic circuit is known from the prior art, for example, where a so-called varicap diode is used as a variable capacitor.
  • the capacitance ofthe varicap diode can be varied in that a reverse bias voltage across the varicap diode is modified.
  • a disadvantage ofthe prior art is that the application of a varicap diode is not always desirable. This is the case, for example, in integrated circuits in which the possibility of integrating a varicap diode into the integrated circuit is not given.
  • the electronic circuit mentioned in the opening paragraph is for this purpose characterized in that the electronic circuit comprises a chain of at least two differential pairs, the tail of each differential pair being connected to a reference terminal ofthe electronic circuit via a separate current source, while each differential pair has a first input and a second input, all said first inputs being coupled to a signal terminal ofthe electronic circuit and all said second inputs being coupled to one another via separate means for providing separate DC voltages between the second inputs.
  • the invention is based on the recognition that the input capacitance of a differential pair can be varied in that the potential of at least one ofthe inputs (first or second) ofthe differential pair is varied.
  • An embodiment of an electronic circuit according to the invention is characterized in that said separate means for providing the separate DC voltages between the second inputs comprise: a chain of resistors connected in series and a controllable current source coupled to the chain of resistors connected in series for controlling said separate DC voltages.
  • the controllable current source delivers a controllable current which flows through the chain of resistors connected in series, so that said separate DC voltages are realized across the resistors.
  • An embodiment of an electronic circuit according to the invention is characterized in that the separate means for providing the separate DC voltages between the second inputs comprise: a chain of resistors connected in series and a controllable voltage source coupled to the chain of resistors connected in series for controlling the separate DC voltages.
  • the separate means for providing the separate DC voltages between the second inputs comprise: a chain of resistors connected in series and a controllable voltage source coupled to the chain of resistors connected in series for controlling the separate DC voltages.
  • An embodiment of an electronic circuit according to the invention is characterized in that the differential pairs comprise field effect transistors.
  • the field effect transistors may be constructed, for example, with MOS transistors.
  • An electronic circuit according to the invention offers the possibility inter alia of realizing frequency-tunable LC oscillators in MOS technology.
  • a coil may be realized, for example, in passive technology or be implemented with a bonding wire of a chip.
  • the tunable LC oscillator may form part, for example, of a phase-locked loop circuit.
  • the electronic circuit according to the invention can be used in electronic circuits of various kinds which require a variable capacitance.
  • Fig. 1 is a circuit diagram of a first embodiment of an electronic circuit for imitating a capacitor with variable capacitance
  • Fig. 2 is a circuit diagram of a second embodiment of an electronic circuit for imitating a capacitor with variable capacitance
  • Fig. 3 is a circuit diagram of a third embodiment of an electronic circuit for imitating a capacitor with variable capacitance.
  • Fig. 1 is a circuit diagram of a first embodiment of an electronic circuit for imitating a capacitor with variable capacitance.
  • the electronic circuit comprises a chain of three differential pairs DFpDF 3 with three separate current sources I 1 -I 3 for the DC adjustment ofthe three differential pairs DF ⁇ -DF 3 , and separate means SPMNS constructed with voltage sources Vi and V 2 .
  • the three separate current sources I ⁇ -I 3 are coupled respectively between the tail ofthe first differential pair DFi and a reference terminal GND, between the tail ofthe second differential pair DF 2 and the reference terminal GND, and between the tail ofthe third differential pair DF 3 and the reference terminal GND.
  • the three differential pairs DF ⁇ -DF are fitted with a first field effect transistor Ti and a second field effect transistor T , a third field effect transistor T 3 and a fourth field effect transistor T 4 , and a fifth field effect transistor T 5 and a sixth field effect transistor T , respectively.
  • the gates ofthe first, third, and fifth field effect transistors Tr, T 3 , T 5 are connected to a signal terminal CPVR ofthe electronic circuit.
  • the gates ofthe second and fourth field effect transistors T 2 , T 4 are interconnected via a voltage source Vi.
  • the gates ofthe fourth and sixth field effect transistors T 4 , T are interconnected via a voltage source V 2 .
  • the tails ofthe first, second, and third differential pairs DF ⁇ -DF 3 are formed by the sources ofthe first and second field effect transistors T ⁇ -T 2 , the sources ofthe third and fourth field effect transistors T 3 -T 4 , and the sources ofthe fifth and sixth field effect transistors T 5 -T 6 , respectively.
  • the electronic circuit operates as follows.
  • a capacitance is formed between the signal terminal CPVR and the reference terminal GND which is the sum ofthe input capacitances ofthe differential pairs DFpDF 3 .
  • the capacitance is determined by the quantity of charge which is transported per voltage unit to the gates ofthe first, third, and fifth field effect transistors T l5 T 3 , T 5 .
  • the transported charge mentioned above will decrease when at least one ofthe voltages supplied by the voltage sources Vi and V 2 increases, with the result that the capacitance between the signal terminal CPVR and the reference terminal GND decreases.
  • the capacitance can thus be varied in that the voltages supplied by the voltage sources Vi and V 2 are varied.
  • An additional advantage ofthe electronic circuit is that the voltage (or voltages), to be varied for varying the capacitance between the signal terminal CPVR and the reference terminal GND do(es) not influence the voltage between the signal terminal CPVR and the reference terminal GND. This is in contrast to the conventional application of a varicap diode as a capacitor with variable capacitance.
  • Fig. 2 is a circuit diagram of a second embodiment of an electronic circuit for imitating a capacitor with variable capacitance.
  • the circuit diagram of Fig. 2 is largely identical to that of Fig. 1.
  • the separate means SPMNS are implemented in the form of a chain CHN RS ⁇ of three resistors R ⁇ -R 3 connected in series and a controllable current source ISRC VR -
  • the separate DC voltages between the gates ofthe second, fourth, and sixth transistors T 2 , T 4 , T 6 are varied in that the current supplied by the controllable current source ISRC VR and flowing through the three resistors RrR 3 connected in series is varied.
  • Fig. 3 is a circuit diagram of a third embodiment ofthe electronic circuit for imitating a capacitor with variable capacitance.
  • the circuit diagram of Fig. 3 is largely identical to that of Fig. 2. In this embodiment, however, the controllable current source
  • ISRC VR is replaced with a controllable voltage source VSRC VR .
  • the chain CHN RS ⁇ in addition comprises a fourth resistor j which is connected in series between the third resistor R 3 and the controllable voltage source VSRC VR .

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Hardware Design (AREA)
  • Networks Using Active Elements (AREA)
  • Semiconductor Integrated Circuits (AREA)

Abstract

An electronic circuit for imitating a capacitor with a controllable capacitance comprises a chain (CHN) of at least two differential pairs (DF1-DF3), the tail of each differential pair (DF1-DF3) being connected to a reference terminal (GND) via a respective separate current source (I1-I3). Each differential pair comprises a first and a second input. All the first inputs of the differential pairs (DF1-DF3) are connected to a signal terminal (CPVR) of the electronic unit. All the second inputs of the differential pairs (DF1-DF3) are interconnected via means (SPMNS) for supplying separate DC voltages between the second inputs of the differential pairs (DF1-DF3). Between the signal terminal (CPVR) and the reference terminal (GND) a capacitance is formed which is the sum of the input capacitances of the differential pairs (DF1-DF3). The capacitance is determined by the amount of charge per unit of voltage which is delivered to the first inputs of the differential pairs (DF1-DF3). If the separate DC voltages between the second inputs of the differential pairs (DF1-DF3) increase, then said amount of charge will decrease and as a consequence the capacitance will decrease. Thus the capacitance can be varied in that said separate DC voltages are varied.

Description

Electronic circuit for imitating a capacitor with variable capacitance.
The invention relates to an electronic circuit for imitating a capacitor with variable capacitance.
Such an electronic circuit is known from the prior art, for example, where a so- called varicap diode is used as a variable capacitor. The capacitance ofthe varicap diode can be varied in that a reverse bias voltage across the varicap diode is modified.
A disadvantage ofthe prior art is that the application of a varicap diode is not always desirable. This is the case, for example, in integrated circuits in which the possibility of integrating a varicap diode into the integrated circuit is not given.
It is an object ofthe invention to provide an electronic circuit for the imitation of a capacitor with variable capacitance which does not require the use of a varicap diode. According to the invention, the electronic circuit mentioned in the opening paragraph is for this purpose characterized in that the electronic circuit comprises a chain of at least two differential pairs, the tail of each differential pair being connected to a reference terminal ofthe electronic circuit via a separate current source, while each differential pair has a first input and a second input, all said first inputs being coupled to a signal terminal ofthe electronic circuit and all said second inputs being coupled to one another via separate means for providing separate DC voltages between the second inputs. The invention is based on the recognition that the input capacitance of a differential pair can be varied in that the potential of at least one ofthe inputs (first or second) ofthe differential pair is varied.
An embodiment of an electronic circuit according to the invention is characterized in that said separate means for providing the separate DC voltages between the second inputs comprise: a chain of resistors connected in series and a controllable current source coupled to the chain of resistors connected in series for controlling said separate DC voltages. A simple implementation ofthe separate means mentioned above is realized thereby. The controllable current source delivers a controllable current which flows through the chain of resistors connected in series, so that said separate DC voltages are realized across the resistors.
An embodiment of an electronic circuit according to the invention is characterized in that the separate means for providing the separate DC voltages between the second inputs comprise: a chain of resistors connected in series and a controllable voltage source coupled to the chain of resistors connected in series for controlling the separate DC voltages. A simple implementation ofthe separate means mentioned above is realized also by these means. It is an alternative solution to the embodiment mentioned in the preceding paragraph, the controllable current source being replaced by a controllable voltage source, while the chain of resistors coupled in series comprises an additional resistor which is connected in series with the controllable voltage source.
An embodiment of an electronic circuit according to the invention is characterized in that the differential pairs comprise field effect transistors. The field effect transistors may be constructed, for example, with MOS transistors. An electronic circuit according to the invention offers the possibility inter alia of realizing frequency-tunable LC oscillators in MOS technology. A coil may be realized, for example, in passive technology or be implemented with a bonding wire of a chip. The tunable LC oscillator may form part, for example, of a phase-locked loop circuit. The electronic circuit according to the invention can be used in electronic circuits of various kinds which require a variable capacitance.
The invention will be explained in more detail with reference to the accompanying drawing, in which:
Fig. 1 is a circuit diagram of a first embodiment of an electronic circuit for imitating a capacitor with variable capacitance,
Fig. 2 is a circuit diagram of a second embodiment of an electronic circuit for imitating a capacitor with variable capacitance; and
Fig. 3 is a circuit diagram of a third embodiment of an electronic circuit for imitating a capacitor with variable capacitance.
Corresponding components or elements have been given the same reference symbols in these Figures.
Fig. 1 is a circuit diagram of a first embodiment of an electronic circuit for imitating a capacitor with variable capacitance. The electronic circuit comprises a chain of three differential pairs DFpDF3 with three separate current sources I1-I3 for the DC adjustment ofthe three differential pairs DFι-DF3, and separate means SPMNS constructed with voltage sources Vi and V2. The three separate current sources Iι-I3 are coupled respectively between the tail ofthe first differential pair DFi and a reference terminal GND, between the tail ofthe second differential pair DF2 and the reference terminal GND, and between the tail ofthe third differential pair DF3 and the reference terminal GND. The three differential pairs DFι-DF are fitted with a first field effect transistor Ti and a second field effect transistor T , a third field effect transistor T3 and a fourth field effect transistor T4, and a fifth field effect transistor T5 and a sixth field effect transistor T , respectively. The gates ofthe first, third, and fifth field effect transistors Tr, T3, T5 are connected to a signal terminal CPVR ofthe electronic circuit. The gates ofthe second and fourth field effect transistors T2, T4 are interconnected via a voltage source Vi. The gates ofthe fourth and sixth field effect transistors T4, T are interconnected via a voltage source V2. The tails ofthe first, second, and third differential pairs DFι-DF3 are formed by the sources ofthe first and second field effect transistors Tι-T2, the sources ofthe third and fourth field effect transistors T3-T4, and the sources ofthe fifth and sixth field effect transistors T5-T6, respectively.
The electronic circuit operates as follows. A capacitance is formed between the signal terminal CPVR and the reference terminal GND which is the sum ofthe input capacitances ofthe differential pairs DFpDF3. The capacitance is determined by the quantity of charge which is transported per voltage unit to the gates ofthe first, third, and fifth field effect transistors Tl5 T3, T5. The transported charge mentioned above will decrease when at least one ofthe voltages supplied by the voltage sources Vi and V2 increases, with the result that the capacitance between the signal terminal CPVR and the reference terminal GND decreases. The capacitance can thus be varied in that the voltages supplied by the voltage sources Vi and V2 are varied.
An additional advantage ofthe electronic circuit is that the voltage (or voltages), to be varied for varying the capacitance between the signal terminal CPVR and the reference terminal GND do(es) not influence the voltage between the signal terminal CPVR and the reference terminal GND. This is in contrast to the conventional application of a varicap diode as a capacitor with variable capacitance.
The adjustment range ofthe electronic circuit is limited by the parasitic capacitances ofthe field effect transistors Tι-T6 to the substrate. The adjustment range ofthe electronic circuit is wider if it is implemented in the SOI technology. This is because said parasitic capacitances are lower then. Fig. 2 is a circuit diagram of a second embodiment of an electronic circuit for imitating a capacitor with variable capacitance. The circuit diagram of Fig. 2 is largely identical to that of Fig. 1. In this embodiment, the separate means SPMNS are implemented in the form of a chain CHNRSΓ of three resistors Rι-R3 connected in series and a controllable current source ISRCVR- The separate DC voltages between the gates ofthe second, fourth, and sixth transistors T2, T4, T6 are varied in that the current supplied by the controllable current source ISRCVR and flowing through the three resistors RrR3 connected in series is varied.
Fig. 3 is a circuit diagram of a third embodiment ofthe electronic circuit for imitating a capacitor with variable capacitance. The circuit diagram of Fig. 3 is largely identical to that of Fig. 2. In this embodiment, however, the controllable current source
ISRCVR is replaced with a controllable voltage source VSRCVR. The chain CHNRSΓ in addition comprises a fourth resistor j which is connected in series between the third resistor R3 and the controllable voltage source VSRCVR.

Claims

CLAIMS:
1. An electronic circuit for imitating a capacitor with variable capacitance, characterized in that the electronic circuit comprises a chain (CHN) of at least two differential pairs (DF1-DF3), the tail of each differential pair (DFι-DF3) being connected to a reference terminal (GND) ofthe electronic circuit via a separate current source (I l ), while each differential pair (DFι-DF3) has a first input and a second input, all said first inputs being coupled to a signal terminal (CPVR) ofthe electronic circuit, and all said second inputs being coupled to one another via separate means (SPMNS) for providing separate DC voltages between the second inputs.
2. An electronic circuit as claimed in claim 1 , characterized in that said separate means (SPMNS) for providing the separate DC voltages between the second inputs comprise: a chain (CFTNRSΓ) of resistors (Rι-R3) connected in series and a controllable current source (ISRCVR) coupled to the chain (CHNRSΓ) of resistors (Rj-R ) connected in series for controlling said separate DC voltages.
3. An electronic circuit as claimed in claim 1 , characterized in that the separate means (SPMNS) for providing the separate DC voltages between the second inputs comprise: a chain (CHNRSΓ) of resistors (Ri-Rt) connected in series and a controllable voltage source (VSRCVR) coupled to the chain (CHNRSΓ) of resistors (Ri-Rt) connected in series for controlling the separate DC voltages.
4. An electronic circuit as claimed in claim 1, 2 or 3, characterized in that the differential pairs (DFι-DF3) comprise field effect transistors (Tj-Tό).
5. An electronic circuit as claimed in claim 4, characterized in that the field effect transistors (Tj-T6) are MOS transistors.
6. An oscillator provided with an electronic circuit as claimed in claim 1, 2, 3, 4,
7. A phase-locked loop provided with an oscillator as claimed in claim 6.
8. An integrated circuit provided with an electronic circuit as claimed in claim 1 , 2, 3, 4, or 5.
9. An integrated circuit provided with an oscillator as claimed in claim 6.
10. An integrated circuit provided with a phase-locked loop as claimed in claim 7.
EP00956297A 1999-08-06 2000-07-26 Electronic circuit for imitating a capacitor with variable capacitance Withdrawn EP1119908A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP00956297A EP1119908A1 (en) 1999-08-06 2000-07-26 Electronic circuit for imitating a capacitor with variable capacitance

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
EP99202594 1999-08-06
EP99202594 1999-08-06
PCT/EP2000/007187 WO2001011773A1 (en) 1999-08-06 2000-07-26 Electronic circuit for imitating a capacitor with variable capacitance
EP00956297A EP1119908A1 (en) 1999-08-06 2000-07-26 Electronic circuit for imitating a capacitor with variable capacitance

Publications (1)

Publication Number Publication Date
EP1119908A1 true EP1119908A1 (en) 2001-08-01

Family

ID=8240529

Family Applications (1)

Application Number Title Priority Date Filing Date
EP00956297A Withdrawn EP1119908A1 (en) 1999-08-06 2000-07-26 Electronic circuit for imitating a capacitor with variable capacitance

Country Status (4)

Country Link
EP (1) EP1119908A1 (en)
JP (1) JP2003506950A (en)
KR (1) KR20010100869A (en)
WO (1) WO2001011773A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10566954B2 (en) 2016-01-21 2020-02-18 Sony Corporation Variable capacitance circuit, oscillator circuit, and method of controlling variable capacitance circuit

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100882293B1 (en) * 2006-07-20 2009-02-10 한국전기연구원 Electromagnetic field reduction demonstration test system using vertical loop

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0111773A1 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10566954B2 (en) 2016-01-21 2020-02-18 Sony Corporation Variable capacitance circuit, oscillator circuit, and method of controlling variable capacitance circuit

Also Published As

Publication number Publication date
WO2001011773A1 (en) 2001-02-15
JP2003506950A (en) 2003-02-18
KR20010100869A (en) 2001-11-14

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