Test structure and probe for differential signals

• US 7,403,028 B2
• Filed: 02/22/2007
• Issued: 07/22/2008
• Est. Priority Date: 06/12/2006
• Status: Expired due to Fees

• Current Assignee: Cascade Microtech Incorporated (FormFactor Incorporated)
• Original Assignee: Cascade Microtech Incorporated (FormFactor Incorporated)
• Inventors: Campbell, Richard
• Primary Examiner(s): Nguyen; Ha
• Assistant Examiner(s): Nguyen; Trung Q.
• Application Number:
  US11/710,149
• Publication Number:
  US 20070285111A1
• Time in Patent Office: 516 Days
• Field of Search: None
• US Class Current: 324/755.03
• CPC Class Codes: G01R 31/2889 Interfaces, e.g. between probe and tester G01R31/31905 and G01R1/07364 take precedence

Abstract

A test structure including a differential gain cell and a differential signal probe include compensation for the Miller effect reducing the frequency dependent variability of the input impedance of the test structure.

Claims

1. A test structure for testing a functionality of a transistor, said test structure comprising:

(a) a first transistor including;

(i) a first terminal connectible through a first resistance to a source of a first component of a differential signal;

(ii) a second terminal connectible through a second resistance to a sink for a first component of an output signal and interconnected to said first terminal by a parasitic capacitance; and

(iii) a third terminal;

(b) a second transistor including;

(i) a first terminal connectible through a third resistance to a source of a second component of a differential signal;

(ii) a second terminal connectible through a fourth resistance to a sink for a second component of an output signal and interconnected to said first terminal by a parasitic capacitance; and

(iii) a third terminal interconnected with said third terminal of said first transistor and a source of a bias voltage;

(c) a first compensating capacitor connecting said first terminal of said first transistor to said second terminal of said second transistor; and

(d) a second compensating capacitor connecting said first terminal of said second transistor to said second terminal of said first transistor.

2. The test structure of claim 1 wherein said first compensating capacitor has a capacitance substantially equal to said parasitic capacitance interconnecting said first terminal of said first transistor and said second terminal of said first transistor and said second compensating capacitor has a capacitance substantially equal to said parasitic capacitance interconnecting said first terminal of said second transistor to said second terminal of said second transistor.

3. The test structure of claim 1 wherein said first, said second, said third and said fourth resistances have values selected to cause said test structure to have a gain approximating unity.