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1. ECE 126
Introduction to Analog Integrated Circuits Design
Lab 5: Current Reference (Constant Gm Current
Reference)

2. TASK
Design your own constant gm current reference. Your design must provide a
constant current using the current spec from lab 1.
** Constant gm current value: 25u
CIRCUIT SCHEMATIC

3. HSPICE CODE

4. CURRENT REFERENCE
.OP RESULT

5. CASCODE BIAS

6. START-UP

7. The figure shows the DC analysis of the Constant gm Current Reference. As seen from
the graph at around 1V, there is indeed a constant current output of 25u.
Id = 25u
VB2
VB1

8. CONCLUSION
A constantgm current sourcehas three parts: the start-up circuit, cascode
bias circuit, and the currentreference circuit.
A start-up circuit plays a very significant role in current reference
circuits.Ideally, thestart-up circuit reliably and predictably provides its kick-start
signal, but then has no impact on the systemafterwards.This justdefines that a
start-up circuit brings out the reference circuit from a dead (zero current)
operating point to its normal operating point and then is no longer used once the
reference circuit starts operating properly.
The Cascode Bias is responsiblefor establishing the operating condition of
the currentreference. The currentreference is designed to attain the target
output currentwhich, in this project, is equivalent to 25μA.
Indeed, this design has produced a current output of 25u. As you can
observethe mosfets are all in the saturation region. Thus we are surethat current
reference is working properly giving a proper out.