In-circuit current measurement

DETAILED DESCRIPTION The present invention provides a method for the accurate and reliable measurement of currents in a circuit without breaking the circuit to insert a measuring device.
The method for measuring current I.
sub.
0 in a circuit includes selecting an element in the circuit having a low resistance with respect to the remainder of the circuit, This element remains connected in the circuit.
A current source is connected in parallel with the element.
The current source has an output current and a current control input for controlling the output current.
A voltage measuring device is connected in parallel with both the element and the current source.
The voltage measuring device has a voltage measurement output for providing a voltage measurement across the element and a voltage measurement control input for controlling the voltage measurement process.
A control device is connected to the current control input and the voltage measurement control input.
A calculation device having a calculation control input is connected to the control device.
A first current I.
sub.
1 is driven through the element with the current source and a first voltage V.
sub.
1 across the element is measured with the measuring device, all in response to the control device.
The first current is at or near zero.
A second current I.
sub.
2 is driven through the element with the current source and a second voltage V.
sub.
2 across the element is measured with the measuring device, all in response to the control device.
The second current is greater than the first current.
A value for the current I.
sub.
0 is calculated with the calculation device in response to the control device according to ##EQU1## The calculated value is provided to a user or to an automated test system in response to the control device.