US 5,254,883 A · Electrical current source circuitry for a bus

Abstract

Electrical current source circuitry for a bus is described. The circuitry includes transistor circuitry coupled between the bus and ground for controlling bus current, control circuitry coupled to the transistor circuitry, and a controller coupled to the control circuitry for controlling the transistor circuitry. The controller comprises a variable level circuit comprising setting circuitry for setting a desired current for the bus and transistor reference circuitry coupled to the setting circuitry. The variable level circuit provides a first voltage. Voltage reference circuitry provides a reference voltage. Comparison circuitry is coupled to the voltage reference circuitry and to the variable level circuit for comparing the first voltage with the reference voltage. Logic circuitry is responsive to a trigger signal from the comparison circuitry. An output of the logic circuitry is coupled to the control circuitry in order to turn on the transistor circuitry in a manner dependent upon an output of the logic circuitry.

Claims39

Dependent claims

Electrical current source circuitry for a bus, comprising:

(A) transistor means coupled between the bus and ground for controlling bus current;
(B) control circuitry coupled to the transistor means;
(C) a controller coupled to the control circuitry for controlling the transistor means, wherein the controller comprises:
(1) a variable level circuit comprising
(a) setting means for setting a desired current for the bus;
and
(b) transistor reference means coupled to the setting means, wherein the variable level circuit provides a first voltage;
(2) voltage reference means for providing a reference voltage;
(3) comparison means coupled to the voltage reference means and the variable level circuit for comparing the first voltage with the reference voltage;
(4) logic means responsive to a trigger signal from the comparison means, wherein an output of the logic means is coupled to the control circuitry in order to turn on the transistor means in a manner dependent upon the output of the logic means.

7 more elements

An output driver for an electronic device coupled to a bus, wherein the bus is coupled to a voltage supply via a termination resistor, wherein the output driver comprises:

(A) a plurality of transistors coupled between the bus and ground for controlling bus current;
(B) control circuitry coupled to gates of the plurality of transistors;
(C) a controller coupled to the control circuitry for controlling the plurality of transistors, wherein the controller comprises:
(1) resistor means coupled to the voltage supply for setting a desired current;
(2) transistor reference means comprising a plurality of transistors coupled between the resistor means and ground, wherein the plurality of transistors of the transistor reference means are selectively turned on to provide a variable voltage;
(3) comparison means coupled to receive the variable voltage for comparing the variable voltage with a reference voltage;
(4) a counter;
and
(5) control logic coupled to (i) the comparison means and (ii) the counter for causing the counter to count until a particular combination of the plurality of transistors of the transistor reference means is turned on by an output of the counter such that the variable voltage is approximately equal to the reference voltage, wherein the output of the counter is also coupled to the control circuitry in order to turn on a particular combination of the plurality of transistors coupled between the bus and ground.

6 more elements

An output driver for an electronic device coupled to a bus, wherein the bus is coupled to a voltage supply via a termination resistor, wherein the output driver comprises:

(A) a plurality of transistors coupled between the bus and ground for controlling bus current;
(B) control circuitry coupled to gates of the plurality of transistors;
(C) a controller coupled to the control circuitry for controlling the plurality of transistors, wherein the controller comprises:
(1) current mirror means coupled to a voltage supply and ground, wherein the current mirror means has an output supplying a current with a predetermined value proportional to a desired current;
(2) capacitor means having a plurality of capacitors selectively coupled to the output of the current mirror means, wherein the capacitor means receives the current from the current mirror means, wherein the capacitor means provides a variable voltage when charged by the current;
(3) comparison means coupled to receive the variable voltage for comparing the variable voltage with a reference voltage;
(4) a counter;
and
(5) control logic coupled to (i) the counter, (ii) the comparison means, and (iii) the output of the current mirror means for causing the capacitor means to be charged to the variable voltage and for causing the counter to start counting when the capacitor means is charged, wherein the control logic causes the counter to count until receiving a trigger signal from the comparison means that indicates that the variable voltage is approximately equal to the reference voltage, wherein an output of the counter is coupled to the control circuitry in order to turn on a particular combination of the plurality of transistors in a manner dependent upon a count of the counter.

6 more elements

Dependencies are inferred from the claim text.

Electrical current source circuitry for a bus

Life of this patent

Electrical current source circuitry for a bus

Life of this patent

Abstract

Claims39