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Process Dependent CMOS Circuit with Digital Outputs

IP.com Disclosure Number: IPCOM000115233D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Gregor, RP: AUTHOR

Abstract

Disclosed is a simple CMOS circuit which provides a set of digital outputs which indicate the effective channel length of the devices on the chip relative to the nominal channel length. This circuit can be used to control source terminated drivers, accurate delay circuits, or other circuits which require constant impedance or delay characteristics independent of the CMOS process variation.

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Process Dependent CMOS Circuit with Digital Outputs

      Disclosed is a simple CMOS circuit which provides a set of
digital outputs which indicate the effective channel length of the
devices on the chip relative to the nominal channel length.  This
circuit can be used to control source terminated drivers, accurate
delay circuits, or other circuits which require constant impedance or
delay characteristics independent of the CMOS process variation.

      The circuit shown in the Figure provides two digital outputs,
one which indicates if the figure provides two digital outputs, one
which indicates if the device channel length is less than the nominal
value, and the second that indicates if the channel length is greater
than nominal.  Device length detection is handled by comparing the
current through a device with a long channel length with the current
through a short channel length device.  The short channel length
device current will vary proportionally with channel length
variations while the long channel length device current will remain
relatively constant.

      The disclosed circuit uses Q5N as the short channel device and
Q4N and Q6N as the long channel devices.  Devices Q1P, Q2P, Q3P, Q1N,
Q2N, and Q3N provide a current mirror to mirror the Q5N current
through Q6N and Q4N.  Tying the gates of Q4N, Q5N, and Q6N keeps the
current in Q4N and Q6N constant.  Therefore, between Q1N and Q4N
(also between Q3N and Q6N) there is a clash of two current sour...