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Current Sink, Source, and Mirror Circuits with Reduced Parameter Variation

IP.com Disclosure Number: IPCOM000121816D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 1 page(s) / 45K

Publishing Venue

IBM

Related People

Braden, JJ: AUTHOR [+5]

Abstract

A method for providing immunity to device parameter variations for accurate constant current sources, sinks, and mirrors is disclosed. The devices used are enhancement MOSFETs which are operated in their resistive region.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 93% of the total text.

Current Sink, Source, and Mirror Circuits with Reduced Parameter
Variation

      A method for providing immunity to device parameter variations
for accurate constant current sources, sinks, and mirrors is
disclosed.  The devices used are enhancement MOSFETs which are
operated in their resistive region.

      The figure shows the schematic of how P and N channel devices
are connected in series to make them operate in their resistive
regions.  The main current sink is the N channel FET T0.  T4 is used
to force T0 operate in its resistive region.  This is due to the fact
that Vds(T0) = Vgs(T0)-Vgs(T4).  Vgs(T4) < Vgs(T0) because T4 is in
saturation due to the fact that Vds(T4) > Vgs(T4)-Vt.  The output
current from T4 and T0 is sent to a P channel current mirror
constructed of TP5 and TP4.  TP2 and TP3 are used to make TP5 and TP4
operate in their resistive regions respectively.  The current from
TP3 and TP4 is dropped across R5 to generate a voltage at the
negative input of the OPAMP.  The positive input of the OPAMP is
driven with a constant voltage (VREF).  Therefore, the net result of
the OPAMP loop is to provide a constant current from both the P and N
channel devices.

      Additional N channel devices like T5 and T6 can be connected to
the loop to generate a constant current sink. Also, if desired, P
channel devices TP6 and TP7 can be connected to the loop to generate
a constant current source. Therefore, the P channel devices are just
mirroring...