Circuit for Measuring Quiescent Current

The following application of common assignee contains some common disclosure, and has the same effective filing date with that of the present application, entitled "Built-in Load Board Design for Performing High Resolution Quiescent Current Measurements of a Device Under Test," docket number TN034, (U.S. Ser. No. 08/547,265) incorporated herein by reference. Accordingly, applicants disclaim the terminal portion of this application after 24 Oct. 2015.

1. Field of the Invention

The present invention relates generally to the testing of integrated circuits, and more specifically, a circuit integrated into a load board for performing high resolution quiescent current measurements of a CMOS integrated circuit (IC) device under test (DUT).

2. Related Art

Due to improper manufacturing or design flaws, integrated circuits (ICs) are subject to a variety of failure modes. Therefore, each IC must be tested to identify any defective circuits before assembly. However, both the complexity and cost of testing an IC are ever increasing with current ICs typically having over 2,000,000 logic gates and over 400 pins.

To respond to the complexity of testing each pin of IC DUT, IDDQ testing was developed. In IDDQ testing, the amount of current the DUT draws is measured on many, test patterns, referred to as vectors. Each such measurement is made when the DUT is in its quiescent state, i.e., after the circuit has time to stabilize after switching.

IDDQ testing is particularly applicable to circuits of CMOS, BiMOS and other technologies that have low quiescent current. The circuits of these technologies may have a relatively high current requirement during switching, but typically have a low quiescent current after the circuit stabilizes. Since a defective circuit may cause the current drawn by a pin of the DUT to increase by orders of magnitude (or be below the expected response), IDDQ testing differentiates defective circuits from good circuits.

One conventional test circuit design and method is illustrated in U.S. Pat. No. 5,371,457 entitled "Method and Apparatus to Test for Current in an Integrated Circuit" (hereinafter the '457 patent). The '457 patent teaches a test circuit for calculating measured currents of an integrated circuit. A problem associated with the '457 patent is that it uses the same power supply for both high/dynamic current requirements during switching (vectors employed while testing the DUT) and low quiescent current after the DUT stabilizes. As a result, large dynamic currents from clocking can create large voltage drops across sense resistors and cause the internal state of the DUT to be incorrect. This, in turn, can cause quiescent current measurements to be invalid.

To attempt to overcome this problem the '457 patent employs a capacitor 22 shown in FIGS. 4-6 and high resistor values (shown as 11, 18 and 21) also in FIGS. 4-6 of the '457 patent. However, the large capacitor slows down the testing process and the larger resistance values reduces measurement resolution.

The present invention avoids the need to employ the same power supply when the DUT is switching (high-powered dynamic supply) and when measuring quiescent current (low current). The quiescent test circuit is capable of supplying high powered voltage to a DUT while the DUT's desired internal state is reached. At this point, the integrated circuit tester, sends an active select signal to the quiescent test circuit instantaneously deselecting the high-powered voltage supply to the DUT and selecting the integrated circuit tester's parametric measurement unit for powering the DUT. The integrated circuit tester, through a parametric measurement unit is capable of measuring the quiescent current of the DUT, while powering the DUT.

The present invention employs a circuit with low valued capacitance and resistors providing high resolution quiescent current measurements. Additionally, the circuit employs less devices than conventional circuits increasing accuracy and decreasing cost of manufacturing the circuit.

A further feature of the present inventions is that the quiescent circuit utilizes segmented voltage planes isolating the test circuit's current from that of the DUT.

FIG. 1 is a high-level block diagram of a load board for testing a Device Under Test, in accordance with a preferred embodiment of the present invention.

FIG. 2 is a block diagram illustrating a combination interface of the integrated circuit tester, the quiescent test circuit, and the Device Under Test shown in FIG. 1.

FIG. 3 is a footprint illustration of circuit components of the quiescent test circuit built into the load board 102.

FIG. 4 is a circuit diagram of the quiescent test circuit according to a preferred embodiment of the present invention.

FIG. 5 is a representative and simplified timing diagram of an example typical quiescent current measurement cycle according to the present invention.

FIG. 6 is a flow chart illustrating operational steps of a typical quiescent current measurement cycle.

FIG. 1 is a high-level block diagram of a load board 102 for testing a Device Under Test (DUT) 104, in accordance with a preferred embodiment of the present invention.

The load board 102 is typically a multi-laminate board having separate conductive signal and power layers to provide separate electrical connections with respective signal pins (male pins not shown, see connection input and output lines 112, 114) and power pins (represented as 128) of the DUT 104.

Viewing FIG. 1 is an external programmable power supply 108, an integrated circuit tester 130 having a Direct Current parametric measurement unit 110, and a quiescent test circuit 106.

The quiescent test circuit 106 is integrated (built-in) into the multi-layer load board 102. The quiescent test circuit 106 is positioned centrally and adjacent to one of the longitudinal ends 150 of the load board 102. Quiescent test circuit 106 measures quiescent current consumption of the DUT 104 via power plane connections 105 to the DUT 104. According to the present invention, quiescent current is directly measured as opposed to calculated from measured voltage levels of DUT 104; using the current sensitive voltage supply V4 from the parametric measurement unit 110 instead of high powered and varied voltage of the external programmable power supply.

External elements such as the external power supply 108 and the tester 130 are easily connected to the load board 102 via voltage connections V1-V4 of the quiescent circuit 106. The external programmable supply 108 is connected to connections V1-V3 via interconnections 117, 119, and 121. The tester 130 via the parametric measurement unit 110 is connected to connection V4 122 on the load board 102 via interconnection line/wire 123.

The integrated circuit tester 130 interfaces to the DUT 104 via load board 102. The tester 130 also interfaces to quiescent test circuit 106 via VDD select 124. The tester 130 is connected to pins of the DUT 104 via input bus 112 and output bus 114. Tester 130 receives quiescent current measurements from the quiescent test circuit 106 as measured by the DC parametric unit 110. In the preferred embodiment tester 130 is a Logic Master XL, High-Performance Test Station of Integrated Measurement Systems, Incorporated, Beaverton, Oreg., U.S.A.

As understood in the art, DUT 104 includes power pins 128 and ground pins 126. Power pins 128 receive power directly from power plate connections 105 in the load board 102. Ground pins 126 are directly connected to a ground plane 134 in the load board 102.

FIG. 2 is a block diagram illustrating a combination interface of the integrated circuit tester 130, the quiescent test circuit 106, and the Device Under Test 104 as shown in FIG. 1. FIG. 2 illustrates how one of two power supplies V1 or V4 is connected to DUT 104 via power plane 105. Tester 130 initially selects DC power supply 108 V1, via VDD select 124. Accordingly, V1 powers the DUT 104, which is a high power supply necessary during clocking operations to be described with reference to FIGS. 5 and 6. Tester 130 alternatively selects DC parametric measurement unit 110 as the power supply via V4, by changing the state of the signal input to VDD select 124. Accordingly, V4 powers the DUT 104, which is a low current power supply used for measuring high resolution static current consumption (quiescent current) of the DUT 104.

Power supplies V2 and V3 are not shown in this diagram, but are connected to quiescent test circuit 106.

Referring to FIG. 3, is a footprint 300 representing the components of the quiescent test circuit 106. Footprint 300 is a section of load board 102 shown in FIG. 1. Footprint 300 is split into two halves: (1) select circuitry 302, and (2) multiplexing (MUX) circuitry 304. Footprint 300 also includes a connection point or node 306 to the power plane connections 105.

Select circuitry 302 includes an open collector OR gate 308 and an open collector NOR gate 310. MUX circuitry 304 includes two independent high power JFET devices 312 and 314.

Select circuitry 302 components 308, 310 are powered by V3 via a V3 voltage plane in the load board 102. MUX circuitry 304 components 312, 314 are powered by V2 via a V2 voltage plane in the load board 102.

In a preferred embodiment, footprint 300 contains individual component footprints for components 308, 310, 312 and 314.

V1 voltage from the external power supply 108 and V4 voltage from the parametric measurement unit 110 are alternatively selected by select circuitry 302 to pass through MUX circuitry 304 to be connected across connection point 306 to power plane 105.

Segmented voltage planes V2 and V3 are employed to perform three functions: (1) to isolate current usage between the DUT 104 and the select circuitry 302 and MUX circuitry 304 (2) to enable direct connections to V2 and V3; and (3) to utilize noise immunity and high current capacity of internal power planes V2 and V3.

Referring to FIG. 4, is a circuit diagram of quiescent test circuit 106 according to a preferred embodiment of the present invention. Components 310, 308, 438, 448 and 442 make up select circuity 302. Resistors 438, 448 and 442 are used for pull-downs to enable by-pass conditions. Notice that V3 is connected to open collector NOR and OR gates 308, 310.

MUX circuitry 304 includes JFETs 312 and 314, decoupling capacitors 408, 410, 436, 418, diodes 424, 426, and resistors 428, 430, 432 and 434. The decoupling capacitors, diodes and resistors act as performance enhancing devices. Notice that V2 is connected to positive side of resistors 430 and 434.

Capacitor 422 represents the variable capacitance level of load board 102, which can be optimized according to the switching speed of the MUX circuitry 304.

Operationally, JFETs 312 and 314, serve as solid state switches to deliver one of two voltage sources V1 or V4. Only one of the JFETs 312 and 314 conduct at a time, with the only exception being a small amount of cross conduction that may occur during the time one JFET is turned off and the other JFET is turned on. Diodes 424 and 426 serve as zener clamps to absorb any voltage transients appearing at the gates of JFETs 312 and 314. Additionally, diodes 424, 426 protect the gates of JFETs 312, 314 should the maximum voltage supply be surpassed. In the preferred embodiment, the maximum recommended voltage is 15 volts.

When the output from NOR gate 310 is in a high impedance state (off), ample voltage appears across resistor 428 to fully turn on transistor 314. During the time transistor 314 is conducting, a voltage appears across resistor 428. This voltage is governed by a resistor divider network of resistors 428, 430. The criteria here is two fold. In the first instance, this network 428, 430 delivers voltage to the gate (G) of transistor 314 to allow the transistor 314 to be fully saturated (lowest resistance from drain to source). In the second case, resistor 428 controls the turn-on speed of transistor 314. The turn-off speed is governed by depleting transistor 314 of its gate turn-on voltage. This occurs when the output of NOR gate 310 changes from its high impedance, to its fully saturated state. V1 402 is the source voltage that is delivered to the DUT 104. Capacitors 408, 410 supply instantaneous current demands of the DUT 104.

Operation of transistor 312 mirrors that of transistor 314 when transistor 314 is not active. Simultaneous operation is prevented due to OR gate 308 being a non-inverting device as opposed to gate 310.

In the preferred embodiment capacitors 408, 410, 418 and 436, typically range between 0.1 uF to 10 uF, resistors 430, 434 are 1 k, resistors 428, 432 are 47 k, resistors 438, 440, 442 can be eliminated but if used between ground optimally range between 10-to-100 ohms.

FIG. 5 is a representative and simplified timing diagram of a typical quiescent current measurement cycle 500 according to the present invention. Measurement cycle includes a clock 502, V1 504, V4, 506, VDD select 508, DUT VDD 510, and Inputs 512 to input pins 112. The quiescent test measurement cycle 500, will be described with reference to the flow diagram of FIG. 6 and elements shown from FIG. 1.

In steps 604-606 the quiescent measurement test begins by sending a predetermined set of data inputs 512 from the tester 130 to the DUT 104. The data inputs 512 are clocked or pulsed-in at the leading edges or rising edges of clock. N successive clock cycles 502 may be needed (typically ranging from 5-to-several thousand) to reach a desired combination of internal node states within the DUT 104. In the example of FIG. 5, there are four clock cycles N-3 through N before the desired internal node state of the DUT 104 is reached.

While clocking and input data occurs in steps 604 and 606, according to block 602, the tester 130 via the VDD select signal 508 (remains as logic zero), which selects V1 504 as voltage source to the DUT 104. While V1 is selected, large dynamic currents from internal switching typically occurs.

Next, in step 608, the DUT reaches a desired internal state. Before the quiescent current is measured, it is necessary to allow any remaining internal switching within the DUT 104 to settle out as indicated by block 610. This phase out period occurs shortly after the falling edge 512 of the Nth clock cycle of clock 502.

In step 612, after the falling edge of the Nth clock 514, the tester 130 via the VDD select signal 508, pulses to a logic 1 and selects V4 506 as the voltage source to the DUT 104. In other words, V4 506 is "pulsed-on" via VDD select going active 515, in step 612.

In step 614, during the high select signal 508, the parametric measurement unit 110, measures the quiescent current consumption of the DUT 104. It should be noted that either current consumption or voltage drops can be measured during step 614, but in the preferred embodiment current consumption is measured.

In step 615, when the tester 130 completes the quiescent current measurement, VDD select returns low 516 or, in other words VDD 508 is pulsed off 516 (inactive or logic zero). After a brief delay the clocking cycles for a new unique combination of internal node states is executed and the process 602-615 repeats.

It should be noted that if changes are made to the circuitry of the DUT, it is possible to perform testing without utilizing the parametric measurement unit 110. By default, VDD select 124 can be ignored (not used) or tri-stated. In this mode, the V1 power supply is always selected regardless of what is presented at the V4 122 input terminal of the quiescent circuit 106. In other words, the quiescent circuit 106 can effectively be made to look like it does not exist.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.