Bi-directional buffer for interfacing test system channel
View Patent ↗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 bi-directional 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.
1. A probe card apparatus comprising:
a plurality of electrical connections to a tester for testing an electronic device;
a plurality of probes disposed to contact the electronic device;
a plurality of communications channels connecting ones of the electrical connections to ones of the probes; and
in a first one of the communication channels, a first amplifier for amplifying a signal output by the electronic device and received at a first one of the probes, the first amplifier providing the amplified signal to a first one of the electrical connections, and
a first by-pass resistor providing a resistive electrical path to the first of the probes by-passing the first amplifier for test signals output by the tester and received at the first one of the electrical connections, wherein:
the first amplifier is biased such that the first amplifier is off in response to a signal driven through the first one of the electrical connections to the first one of the probes, and
the first amplifier is biased such that the first amplifier is on in response to a signal driven through the first one of the probes to the first one of the electrical connections.
2. The probe card apparatus of claim 1 , wherein the first amplifier is a current amplifier for amplifying a current of the signal output by the electronic device.
3. The probe card apparatus of claim 2 further comprising a power supply for supplying power to the first amplifier, the power having a voltage component sufficient for the amplifier to operate and the power having an additional voltage component sufficient to compensate for a voltage drop across the first amplifier.
4. The probe card apparatus of claim 1 further comprising:
a plurality of second amplifiers each for amplifying one of a plurality of second signals output by the electronic device and received at one of a second of the probes, each of the second amplifiers providing the one of the amplified second signals to one of a second plurality of electrical connections to the tester; and
a plurality of second by-pass electrical paths each for providing an electrical path to one of the second of the probes by-passing one of the second amplifiers for test signals output by the tester and received at one of the second electrical connections to the tester.
5. The probe card apparatus of claim 1 , wherein the first communication channel is bi-directional.
6. The probe card apparatus of claim 1 , wherein the first communication channel is passively bi-directional.
7. The probe card apparatus of claim 1 , wherein the by-pass resistor is part of a by-pass path that is unswitched.
8. A probe card apparatus comprising:
a plurality of electrical connections to communications channels to a tester for testing an electronic device;
a plurality of probes disposed to contact the electronic device;
in a first communication channel, a first amplifier for amplifying a signal output by the electronic device and received at a first of the probes, the first amplifier providing the amplified signal to a first of the communications channels;
a first by-pass electrical path for providing an electrical path to the first of the probes by-passing the first amplifier for test signals output by the tester and received at the first connection to the first of the communications channels;
a temperature sensor; and
a power supply circuit connected to the temperature sensor, the power supply circuit providing a voltage to the first amplifier that varies with a temperature sensed by the temperature sensor.
9. The probe card apparatus of claim 8 further comprising a memory connected to the power supply circuit for storing data correlating temperature versus voltage to the first amplifier.
10. A method of testing an electronic device, the method comprising:
providing a plurality of test signals from a tester for controlling testing of the electronic device through a probe card apparatus comprising a plurality of communications channels between the tester and the electronic device, the providing comprising providing one of the test signals through a first by-pass resistor by-passing an amplifier disposed in a first one of the communications channels to a first probe in contact with the electronic device; and
amplifying an output signal output by the electronic device and received at the first probe with the amplifier to produce an amplified signal; and
providing the amplified output signal to the tester through the first communications channel,
wherein the first by-pass resistor by-passes the first amplifier.
11. The method of claim 10 , wherein the amplifying comprises amplifying a current of the output signal.
12. The method of claim 11 further comprising providing power to the first amplifier, the power having a voltage component sufficient for the amplifier to operate and the power having an additional voltage component sufficient to compensate for a voltage drop across the first amplifier.
13. The method of claim 10 , wherein the providing a plurality of test signals further comprises providing ones of the test signals through second by-pass paths of second ones of the communications channels to second probes in contact with the electronic device; and
amplifying output signals output by the electronic device and received at the second probes; and
providing the amplified output signals to the tester through the second communications channels,
wherein the second by-pass paths by-pass the second amplifiers.
14. The method of claim 10 further comprising selectively connecting an output of the first amplifier through a resistor to ground.
15. The method of claim 10 further comprising selectively providing a current sink path from an output of the first amplifier.
16. A method of testing an electronic device, the method comprising:
providing a plurality of test signals from a tester for controlling testing of the electronic device through ones of communications channels between the tester and the electronic device, the providing comprising providing one of the test signals through a first by-pass path of a first of the communications channels to a first probe in contact with the electronic device;
amplifying an output signal output by the electronic device and received at the first probe;
providing the amplified output signal to the tester through the first communications channel, wherein the first by-pass path by-passes the first amplifier;
sensing a temperature adjacent the first amplifier; and
varying a voltage component of power supplied to the first amplifier in accordance with the sensed temperature.