Bi-directional buffer for interfacing test system channel

• US 20060132158A1
• Filed: 12/21/2004
• Published: 06/22/2006
• Est. Priority Date: 12/21/2004
• Status: Active Grant

• Current Assignee: FormFactor Incorporated
• Original Assignee: FormFactor Incorporated
• Inventors: Miller, Charles A.
• Granted Patent: US 7,262,624 B2
• Time in Patent Office: Days
• US Class Current: 324/754.70
• CPC Class Codes: G01R 31/2889 Interfaces, e.g. between probe and tester G01R31/31905 and G01R1/07364 take precedence
• CPC Class Codes: G01R 31/31713 Input or output interfaces for test, e.g. test pins, buffers for scan test G01R31/318572

Abstract

An emitter follower or source follower transistor is provided in the channel of a wafer test system between a DUT and a test system controller to enable a low power DUT to drive a test system channel. A bypass resistor is included between the base and emitter of the emitter follower transistor to enable bidirectional signals to be provided between the DUT channel and test system controller, as well as to enable parametric tests to be performed. The emitter follower transistor and bypass resistor can be provided on the probe card, with a pull down termination circuit included in the test system controller. The test system controller can provide compensation for the base to emitter voltage drop of the emitter follower transistor.

Claims

1. A probe card comprising a voltage follower amplifier provided in a test channel.

2. The probe card of claim 1, wherein the voltage follower amplifier comprises an emitter follower transistor.

3. The probe card of claim 1 further comprising a bypass resistor provided in parallel with the voltage follower amplifier.

4. The probe card of claim 1, wherein the voltage follower amplifier comprises:

an emitter follower transistor having a base connected to a portion of the channel for connecting to a DUT, an emitter for connecting to a portion of the channel for connecting to a test controller, and a collector; and

a bypass resistor connecting the base to the emitter of the emitter follower transistor.

5. The probe card of claim 1, wherein the collector of the emitter follower transistor is connected to receive a system power supply voltage plus a voltage approximately equal to the base to emitter offset voltage of the emitter follower transistor.

6. The probe card of claim 1, further comprising:

a temperature sensor; and

a power supply circuit connected to the temperature sensor, the power supply circuit providing a voltage to the collector of the emitter follower transistor with compensation for base-emitter voltage change of the emitter follower transistor due to temperature change as indicated by the temperature sensor.

7. The probe card of claim 1, wherein the voltage follower amplifier comprises a source follower transistor.

8. A device tested using the probe card of claim 1.

9. An apparatus comprising a voltage follower amplifier provided in the channel of a test system for connecting a DUT to a test system controller.

10. The apparatus of claim 9, wherein the voltage follower amplifier comprises an emitter follower including a transistor having a base connected to a portion of the channel for linking to the DUT, and an emitter connected to a portion of the channel for linking to the test system controller.

11. The apparatus of claim 10, further comprising a bypass resistor connecting the base and emitter of the emitter follower transistor.

12. The apparatus of claim 11, further comprising a switch for selectively connecting the emitter of the emitter follower transistor through a resistor to ground.

13. The apparatus of claim 11, wherein the test system controller can be programmed to selectively provide a current sink path from the emitter of the emitter follower transistor.

14. The apparatus of claim 11, wherein the test system controller comprises:

a driver buffer connected by a resistor to the emitter of the emitter follower transistor, the driver buffer configured to provide a voltage to compensate for the base to emitter voltage of the emitter follower transistor; and

a comparator buffer connected to the emitter of the emitter follower transistor.

15. The apparatus of claim 11, wherein the collector of the emitter follower transistor is connected to a system test system Vdd plus a voltage approximately equal to the base to emitter voltage of the emitter follower transistor.

16. The apparatus of claim 11 further comprising a means to compensate for a base to emitter voltage drop of the emitter follower transistor.

17. The apparatus of claim 16, wherein the means to compensate comprises:

a temperature sensor; and

a power supply circuit connected to the temperature sensor, the power supply circuit providing a voltage to the collector of the emitter follower transistor with compensation for the base to emitter voltage drop as well as change in the base to emitter voltage due to a temperature change as indicated by the temperature sensor.

18. The apparatus of claim 16, wherein the means to compensate further comprises:

a memory connected to the power supply circuit for storing a calibration of base to emitter voltage drop versus temperature.

19. The apparatus of claim 9 included in a test system controller.

20. The apparatus of claim 12 included in a probe card.