Download CIRCUIT IDEAS FOR DESIGNERS This current source can be built

Category: Current Source
CIRCUIT IDEAS FOR DESIGNERS
Schematic no. cs_11003.0
Current Source Mirror
Description
This current source can be built within a single IC package. The high input gate impedance of Q1
and Q2 eliminates any gate leakage current considerations in most cases, resulting in equal gate
voltages of Q1 and Q2. Substantially all of the ISET current becomes the drain current of Q1. Drain
current of Q2 is mirrored to that of drain current of Q3. Again, very low gate leakage currents of
Q3 and Q4 assures that gate voltages of Q3 and Q4 are equal. When drain voltage of Q4 is at drain
voltage of Q3, drain current of Q4 (ISOURCE) is equal to drain current of Q3. Efforts should be made
to set drain voltage values of Q1 and Q2 as close to each other possible. Likewise, drain voltages
of Q3 should be equal to that of Q4. If these voltages are significantly different from each other,
then a cascode current source configuration should be considered.
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