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US 6,356,141 B1Granted
Constant-current output circuit
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorHiroyuki Yamauchi
Life of this patent
Estimating the term…
Abstract
A driver having a CMOS configuration is connected to a twisted-pair cable so as to perform data transmission by making a change in the direction in which a constant current flows to the cable having two signal lines each coupled to a bias voltage through a terminating resistor. A gate voltage control circuit makes utilization of a detected bias voltage and voltage drops in replica transistors each forming a replica of the terminating resistor for controlling the gate voltage of PMOS and NMOS drive transistors in the driver, whereby the drain current of each of these drive transistors is held at a fixed value.
Claims19
A constant-current output circuit for outputting a constant current to a cable coupled to a bias voltage through a terminating resistor, said constant-current output circuit comprising:
- a drive transistor having a gate electrode, a source electrode coupled to a power supply, and a drain electrode coupled to said cable;
- and
- adjustment means for adjusting the current drive capability of said drive transistor so that when a voltage between said drain electrode and said source electrode undergoes a variation due to a change in said bias voltage, a variation in drain current of said drive transistor accompanied by said drain-source voltage variation is compensated such that said drain current of said drive transistor is maintained at a substantially same level so as to generate said constant current,
- wherein said adjustment means has a function of adjusting, based on system information indicative of a prediction of the change in said bias voltage, the current drive capability of said drive transistor.
1 more element
A constant-current output circuit for outputting a constant current to a cable coupled to a bias voltage through a terminating resistor, said constant-current output circuit comprising:
- a drive transistor having a gate electrode, a source electrode coupled to a power supply, and a drain electrode coupled to said cable;
- and
- adjustment means for adjusting the current drive capability of said drive transistor so that when a voltage between said drain electrode and said source electrode undergoes a variation due to a change in said bias voltage, a variation in drain current of said drive transistor accompanied by said drain-source voltage variation is compensated such that said drain current of said drive transistor is maintained at a substantially same level so as to generate said constant current,
- wherein said adjustment means has a gate voltage control circuit for voltage control of said gate electrode of said drive transistor,
- said gate voltage control circuit having:
- means for detecting said bias voltage, said detecting means comprising said terminating resistor;
- a series circuit disposed between said power supply and a reference node and constructed of a replica transistor forming a replica of said drive transistor and a replica resistor forming a replica of said terminating resistor;
- a current source from which a constant current flows into said series circuit;
- and means for making a comparison between a voltage at said reference node and said detected bias voltage, for controlling, based on a result of said comparison, a gate voltage of said replica transistor, and for providing said controlled gate voltage to said gate electrode of said drive transistor.
6 more elements
A constant-current output circuit for outputting a constant current to a cable coupled to a bias voltage through a terminating resistor, said constant-current output circuit comprising:
- a drive transistor having a gate electrode, a source electrode coupled to a power supply, and a drain electrode coupled to said cable;
- and
- adjustment means for adjusting the current drive capability of said drive transistor so that when a voltage between said drain electrode and said source electrode undergoes a variation due to a change in said bias voltage, a variation in drain current of said drive transistor accompanied by said drain-source voltage variation is compensated such that said drain current of said drive transistor is maintained at a substantially same level so as to generate said constant current,
- wherein said adjustment means has a gate voltage control circuit for voltage control of said gate electrode of said drive transistor,
- said gate voltage control circuit having:
- means for detecting said bias voltage;
- a replica transistor, disposed between said power supply and a reference node, for forming a replica of said drive transistor;
- a current source from which a constant current flows into said replica transistor;
- a variable voltage generation circuit for generating, from said detected bias voltage, a variable voltage wherein a difference of said variable voltage with respect to said bias voltage represents a voltage drop across said terminating resistor;
- and
- means for making a comparison between a voltage at said reference node and said generated variable voltage, for controlling, based on a result of said comparison, a gate voltage of said replica transistor, and for providing said controlled gate voltage to said gate electrode of said drive transistor.
8 more elements
A constant-current output circuit for outputting a constant current to a cable coupled to a bias voltage through a terminating resistor, said constant-current output circuit comprising:
- a driver including a plurality of drive transistors having respective gate electrodes, source electrodes coupled to a power supply common thereto, and drain electrodes coupled in common to said cable;
- and
- adjustment means for adjusting the current drive capability of said driver so that when a voltage between said common drain electrode and said common source electrode undergoes a variation due to a change in said bias voltage, a variation in output current of said driver accompanied by said drain-source voltage variation is compensated thereby to establish a substantial correspondence between said output current of said driver and said constant current.
A data transmission system comprising:
- a cable coupled to a bias voltage through a terminating resistor;
- and
- a constant-current output circuit for outputting a constant current to said cable;
- said constant-current output circuit having:
- a drive transistor having a gate electrode, a source electrode coupled to a power supply, and a drain electrode coupled to said cable;
- and
- adjustment means for adjusting the current drive capability of said drive transistor so that when a voltage between said drain electrode and said source electrode undergoes a variation due to a change in said bias voltage, a variation in drain current of said drive transistor accompanied by said drain-source voltage variation is compensated such that said drain current of said drive transistor is maintained at a substantially same level so as to generate said constant current,
- wherein said adjustment means has a gate voltage control circuit for voltage control of said gate electrode of said drive transistor,
- said gate voltage control circuit having;
- means for detecting said bias voltage, said detecting means comprising said terminating resistor;
- series circuit disposed between said power supply and a reference node and constructed of a replica transistor forming a replica of said drive transistor and a replica resistor forming a replica of said terminating resistor;
- a current source from which a constant current flows into said series circuit;
- and means for making a comparison between a voltage at said reference node and said detected bias voltage, for controlling, based on a result of said comparison, a gate voltage of said replica transistor, and for providing said controlled gate voltage to said gate electrode of said drive transistor.
10 more elements
A data transmission system comprising:
- a cable coupled to a bias voltage through a terminating resistor;
- and
- a constant-current output circuit for outputting a constant current to said cable;
- said constant-current output circuit having:
- a driver including a plurality of drive transistors having respective gate electrodes, source electrodes coupled to a power supply common thereto, and drain electrodes coupled in common to said cable;
- and
- adjustment means for adjusting the current drive capability of said driver so that when a voltage between said common drain electrode and said common source electrode undergoes a variation due to a change in said bias voltage, a variation in output current of said driver accompanied by said drain-source voltage variation is compensated such that said output current of said driver is maintained at a substantially same level so as to generate said constant current.
4 more elements
Dependencies are inferred from the claim text.