Islamic university –Gaza

Electrical Engineering

Electronic II Lab

Experiment (3)Current Mirror + Darlington

Instructors:Eng. Samah K. Qalaja

Eng. Mohammed S. AbuwardaFall-2017

Part One: Current Mirror

A current mirror is used to replicate the

current from a current source to other locations

Current mirror circuit consists of two back-to-back npntransistors .

The controlling(Ref.) current is the collector current of Q1.

Q1 and Q2 are assumed to be a “matched”

The controlling element is R. RII cR /)7.010(1

Calculations

If the collector and base of QREF are not shorted together, there will not be a path for the base currents to flow, so that Icopy is zero.

Note:

Practical

Build the circuit shown in figure

Measure the value of Iref and Iload

IloadIrefRL

100

1k

2.2k

3.3k

For Rx=3.3k

IloadIrefRx (+470)

100

1k

2.2k

3.3k

10k

For RL=1k

Part Two: Darlington Connection

This configuration gives a much higher current gain

and unity voltage gain.

Calculations

cc B1 B E2 B

E1 B2 E2B1

1 1 1 2

E2 1 2 B1 B1

1 2

V +I R 1.4 I R 0

I I II

I I I

Super Beta

D

D

DC AnalysisPractical

E

B

I =

I =

AC Analysis

vA =