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Positive Temperature Coefficient Current Source in Plain CMOS Technology

IP.com Disclosure Number: IPCOM000114674D
Original Publication Date: 1995-Jan-01
Included in the Prior Art Database: 2005-Mar-29
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Andoh, H: AUTHOR

Abstract

In CMOS circuits it is sometimes needed to have a current source with a positive temperature coefficients in order to maintain a constant Gm of a FET over the range of temperature, in other words the subject current source is required to compensate for the Gm degradation with rising temperature in order to maintain a constant Gm.

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Positive Temperature Coefficient Current Source in Plain CMOS Technology

      In CMOS circuits it is sometimes needed to have a current
source with a positive temperature coefficients in order to maintain
a constant Gm of a FET over the range of temperature, in other words
the subject current source is required to compensate for the Gm
degradation with rising temperature in order to maintain a constant
Gm.

      It is easy to get a negative temp.  coefficient current by
using a NWELL resistor or a Source/Drain resistor, which has a
positive temperature coefficient.  This invention is to get the
subject with a combination of the above current sources.

      Circuit operation - This system comprises one temp.compensated
voltage source (1), two OP Amps (2,3), a pair of FETs (4) that are
sized 1to N, a pair of PFETs (5) that are sized 1 to M, a Nwell
resistor R1 (6), a Source/Drain resistor R2 (7), and 4 same sized
FET's Q5,Q6,Q7,and Q8 (8).

      Suppose a Nwell resistor has Tc1 temp.coefficient and a
Source/Drain resistor has Tc2 temp.coefficient.  Then the current
which runs through Q8 can be expressed as follows with the FET
pattern sizes taken into considerations.
   IQ8 = <N*Vref> over <R10> (1-Tc1*(T-Ta)) -
          <M*Vref> over <R20> (1-Tc2*(T-Ta))
  where T is the measurement temp.  and Ta is the temp.  at which R1
was measured as R10, and R2 as R20.

Differentiating the above IQ8 expression by temp.  one gets
   <d IQ8> over <d...