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ON-CHIP CAPACITANCE MEASUREMENT METHOD

IP.com Disclosure Number: IPCOM000006230D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2001-Dec-17
Document File: 2 page(s) / 68K

Publishing Venue

Motorola

Related People

Dejan Mijuskovic: AUTHOR

Abstract

The method, and the associated circuitry described below can be used for measurements of small on-chip capacitances. The value Cut of the Capacitor Under Test (CUT) is converted into DC current by the on- chip circuitry. The measurement of the current is then performed off-chip, and does not require clean AC environment. Therefore, the method can be used in Lab setups, probe, and final test. The area of applica- tion includes Lab characterizations, monitoring of the process parameters, trimming of RC constants (mea- sure C, trim R), etc. Accuracy of the procedure depends upon available accuracies for measurements of voltage and current, and upon the technology used to process the chip.

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MOlWROLA INC. Technical Developments Volume 13 July 1991

ON-CHIP CAPACITANCE MEASUREMENT METHOD

by Dejan Mijuskovic

INTRODUCTION

  The method, and the associated circuitry described below can be used for measurements of small on-chip capacitances. The value Cut of the Capacitor Under Test (CUT) is converted into DC current by the on- chip circuitry. The measurement of the current is then performed off-chip, and does not require clean AC environment. Therefore, the method can be used in Lab setups, probe, and final test. The area of applica- tion includes Lab characterizations, monitoring of the process parameters, trimming of RC constants (mea- sure C, trim R), etc. Accuracy of the procedure depends upon available accuracies for measurements of voltage and current, and upon the technology used to process the chip.

DESCRIPTION OF THE METHOD

  The method is based on the measurement of the average current taken from VDD due to switching of capacitances (Figure). In the first step SEL=O, and TGO is on, while TGl is off. The average Idd of the inverter (IavO) is measured.

  In the second step, SEL=l, TGO is off, and TGl is on.' Now, the inverter is loaded with the CUT. Average Idd of the inverter (Iavl) is measured again.

These two currents are given by: IavO = Imsh + fck x Vdd x (Cp + CpO), and

Iavl = Irush + fck x Vdd x (Cp t Cpl + Cut)

Solving for Cut yields:

Cut = (Iavl - IavO)/(fck x Vdd) + CpO - Cpl

  The procedure assumes that the inverter rush cur- rents are equal...