Programmable function generator

Claim 2

A programmable function generator comprising: current ladder means including a pair of terminals, a plurality of impedances in series having nodes therebetween and a plurality of matched current source means each connected to one only of said nodes for delivering current to said ladder; current driver means for drawing complementary currents from said ladder means through said pair of terminals adding to a constant value and varying said currents for causing a voltage peak to move along said ladder means; a plurality of output means, each including programmable impedance means for producing an output determined by current flow through said impedance means; a plurality of transistor means each connected to one only of said nodes and one only of said output means and drawing current from said ladder responsive to said voltage peak for enabling current flow from selected ones of said output means; and regulating means drawing current from said ladder means and responsive thereto for regulating said current source means to maintain the total current delivered to said ladder means equal to the current required By the means drawing current from said ladder means.

Claim 3

The generator of claim 1 wherein said plurality of output means are connected to means for converting said output to a voltage.

Claim 4

The generator of claim 1 wherein said current driver means is responsive to an externally applied signal to vary said complementary currents as a linear function of said external signal.

Claim 5

The generator of claim 1 wherein said current driver means includes temperature compensating means for maintaining the total current from said ladder means at said constant value.

Claim 6

The generator of claim 1 wherein said generator includes an additional current source means for sinking said current from said output means and said additional current source means has feedback means for maintaining said current from said plurality of output means constant.

Claim 7

The function generator of claim 1 further including voltage limiter means for diverting current from a central node of said ladder means when the voltage from either of said pair of terminals to said central node approaches the reverse breakdown voltage of any of said transistor means.

Claim 8

The function generator of claim 5 wherein said feedback means includes means for compensating the current flow from said plurality of output means against variations due to temperature; and means for maintaining the current flow from said output means to said transistor means constant so that during transitions from a first output means to a second output means said output will be a linear interpolation between the values of the output from said first and second output means.

Claim 9

The generator of claim 4 wherein said current driver means further includes means for causing the complementary flow from said terminals of said ladder means to shift linearly between said terminals.

Claim 10

A function generator comprising: a series impedance means having a plurality of impedance means connected in series between a pair of terminals and defining circuit node points at said terminals and between said impedance means; a plurality of matched current source means for providing equal currents and each connected to one only of said circuit node points to supply said equal currents to said ladder; current driver means for providing flow of complementary current from said ladder through said pair of terminals in response to an externally applied signal to provide a voltage peak in said ladder at a circuit node or at two of said nodes of said ladder, and for controlling said complementary currents to determine the position of said voltage peak along said ladder; a plurality of unidirectional conducting means each connected between one only of said nodes and a third terminal of said ladder to provide for current flow through said third terminal from said circuit node or nodes which are at said voltage peak; regulating means responsive to current flow through said third terminal for controlling said matched current source means to maintain the current from said node or nodes which are at said voltage peak to said third terminal equal to the current from one only of said matched current source means; and a plurality of output control means each connected to one only of said node points and responsive to the voltage at the corresponding one of said node points.

Claim 11

A function generator comprising: a series impedance means having a plurality of impedance means connected in series between a pair of terminals and defining circuit node points at said terminals and between said impedance means; a plurality of matched current source means for providing equal currents and each connected to one only of said circuit node points to supply said equal currents to said ladder; current driver means for providing flow of complementary current from said ladder through said pair of terminals in response to an externally applied signal to provide a voltage peak in said ladder at a circuit node or at two of said nodes of said ladder, and for controlling said complementary currents to determine the position of said voltage peak along said ladder; a plurality of unidirectional conducting means each connected between one only of said nodes and a third terminal of said ladder to provide for current flow through said third terminal from said circuit node or nodes which are at said voltage peak; regulating means responsive to current flow through said third terminal for controlling said matched current source means to maintain the current from said node or nodes which are at said voltage peak to said third terminal equal to the current from one only of said matched current source means; and a plurality of output control means each connected to one only of said node points and responsive to the voltage at the corresponding one of said node points.

Claim 12

The function generator according to claim 9 in which said impedance means each comprise a pair of diodes which are connected in parallel and for conduction in opposite directions.

Claim 13

The function generator according to claim 9 in which said output control means comprise transistors having a control element connected to the corresponding one of said node points and drawing current from said ladder responsive to said voltage at said one node.

Claim 14

The function generator according to claim 11 which also includes voltage limiter means for diverting current from a central node of said ladder when the voltage from either of said pair of terminals to said central node approaches The reverse breakdown voltage of any of said transistors.

Claim 15

The function generator according to claim 11 in which said regulating means comprises: a pair of matched impedances; an additional matched current source means; and differential amplifier means responsive to the difference between voltages produced by current flow from said third terminal through one of said matched impedances and current flow from said additional current source means through the other of said matched impedances for regulating the current output of each of said plurality of matched current source means to maintain the total current from said ladder through said third terminal and said transistors equal to the current from one of said matched current source means.

Claim 16

The function generator according to claim 9 including means to supply an input control current derived from said externally applied signal to said current driver, said current driver having means responsive to said input control current to vary said complementary currents as a linear function of said input control current.