Method and apparatus for remotely buffering test channels

• US 7,825,652 B2
• Filed: 11/18/2008
• Issued: 11/02/2010
• Est. Priority Date: 09/09/2004
• Status: Expired due to Fees

• Current Assignee: FormFactor Incorporated
• Original Assignee: FormFactor Incorporated
• Inventors: Miller, Charles A.
• Primary Examiner(s): Tang; Minh N
• Assistant Examiner(s): Nguyen; Trung Q
• Application Number:
  US12/273,408
• Publication Number:
  US 20090132190A1
• Time in Patent Office: 714 Days
• Field of Search: 324/158.1, 324/715, 324/751, 324/752, 324/76.36, 324763-765, 324/508, 324/609, 324/66, 324/713, 324/244, 324/253, 714/727, 714/704, 714/709, 714/735, 257/115, 257/157, 257/190, 257/160
• US Class Current: 324/750.3
• CPC Class Codes: G01R 31/3008 Quiescent current [IDDQ] test or leakage current test

Abstract

A system is provided to enable leakage current measurement or parametric tests to be performed with an isolation buffer provided in a channel line. Multiple such isolation buffers are used to connect a single signal channel to multiple lines. Leakage current measurement is provided by providing a buffer bypass element, such as a resistor or transmission gate, between the input and output of each buffer. The buffer bypass element can be used to calibrate buffer delay out of the test system by using TDR measurements to determine the buffer delay based on reflected pulses through the buffer bypass element. Buffer delay can likewise be calibrated out by comparing measurements of a buffered and non-buffered channel line, or by measuring a device having a known delay.

Claims

1. A method of measuring the delay of a buffer in a test circuit, the method comprising:

providing a signal pulse through the buffer;

measuring the signal pulse as reflected from a buffer bypass element provided between an input and output of the buffer; and

determining the delay introduced by the buffer from the reflected signal pulse using a time domain reflectometer calculation.

2. The method of claim 1, wherein the buffer output is connected to a test probe.

3. A method of measuring the delay of a buffer in a test circuit, wherein the buffer is provided in a first transmission line, the method comprising:

measuring delay of the first transmission line and the buffer;

measuring delay of a second transmission line substantially similar to the first transmission line without a buffer; and

calculating the delay through the buffer by determining a difference between a delay through the first transmission line with the buffer and the delay through the second transmission line.

4. The method of claim 3, wherein a buffer bypass element is provided between an input and an output of the buffer.

5. A method of calibrating out a delay of a buffer in a test circuit, the method comprising:

measuring a delay of a device having a known delay using the test device with the buffer; and

calibrating out the delay of the buffer by comparing the measured delay of the device with the known delay.

6. The method of claim 5, wherein a buffer bypass element is provided between an input and an output of the buffer.