EE 2212
EXPERIMENT 8
4 December 2014
THE EMITTER-COUPLED PAIR
Note 1: No report required. Your Experiment 8 effort is to be included in
your notebook
Note 2: We will use the laboratory time slot on
Thursday, 11 December, for individual notebook reviews. Schedule to beposted
for 10 minute time slots.
Note 2: The CA 3046 is the same electrically as the
LM 3046. Just a different manufacturer.
PURPOSE
Ø
The
purpose of this experiment is to characterize the properties of an emitter-coupled pair
(DC transfer characteristics and AC gain measurements).
COMPONENTS
Ø
LM3046/CA3046
transistor array. The data sheet is
posted on the class WEB page
Ø
20
kW resistors for the collector resistors which should be reasonably well matched
Ø
4.7
kW resistor for the input voltage divider
Ø
47 W resistor for the input voltage divider
GENERAL INFORMATION
Ø In IC biasing networks, it is essential
that transistors be well matched and parameter variations track with
temperature. Figure 1 is a pin out of the
LM3046/CA3046 Transistor Array. Observe that you MUST connect Pin 13, the IC
substrate, to
the most negative point in the circuit or bad things happen to the IC.
Figure 1 LM3046/CA3046 NPN BJT
ARRAY
Use Figure 2 and class notes for guidance to
prepare a detailed circuit diagram.
Include pinouts
for the LM3046/CA3046 npn array. From your circuit diagram and circuit
specifications, calculate the expected important Q-point values and Adm .
DC MEASUREMENTS
Refer to the diagram and data
sheet of the LM 3046/CA3046 BJT array.
Set up the circuit in Figure 2 using Q1 and Q2 for
the emitter-coupled pair. Select a value
for REE such that the DC values for Vo1 and Vo2 are about 5 volts. Ground both the inputs of Q1 and Q2. Measure
the all Q-point voltages and currents using the DMM. Use the oscilloscope to also check for
excessive noise which may translate as a noisy dc voltage measurement. Pay particular attention to VOD.
Since the transistors and resistors are reasonably well matched, you would
expect VOD = 0 or reasonably close. If VOD is larger than
a few tens of mV, check your circuit and/or match the collector resistors
better. Lead dress and length is also
important. Be neat! Compare your Q-point values with the expected
and PSPICE simulations. In addition to
using the DMM, look for excessive noise using the scope even though you are
measuring a dc voltage.
Figure 2
TRANSFER CHARACTERISTICS
The transfer characteristics of
a circuit can be displayed using the X-Y oscilloscope inputs. The amplitude of
the input must be large enough to drive the input through the entire desired range
of operation. You are particularly interested in the VOD versus VID
characteristic. Use a low frequency sinusoid or triangular wave as the input.
From a practical viewpoint, if the input signals are noisy because of low
amplitudes, you will choose to use an input voltage divider to provide
"cleaner" waveforms. Note the 100:1 voltage divider input drive
circuit shown in Figure 2, although it
doesn’t have to be 100:1. The signal
generators have a 100 mV minimum. By
using a 100:1 external divider, you can achieve a relatively noise free signal
at the input to the BJT bases. Keep
track of the divider ratio you finally use to scale your measurement correctly.
Also observe that because the oscilloscope does not have a floating input (i.e.,
one side of each oscilloscope input is connected to ground), you will have to
measure either VO1 or VO2 and scale the final results
accordingly by a factor of 2 and also do not forget the sign (180°phase)
differences for each of the outputs.
Show that the slope of the
transfer characteristic will be equal to |Adm/2|.
Compare your results to a SPICE simulation.
DIFFERENTIAL-MODE OPERATION
Set up your input signals, use
1 kHz, so that the output is reasonably linear. You will need some level of voltage
division as shown in the figure. The
figure illustrates a 100:1 divider but the actual divider value is not
critical. Use the oscilloscope and DMM
to measure the differential-mode voltage gain. Compare your results to your
calculations and a SPICE simulation. Include the effect of
a non-infinite Early voltage to improve your analysis and simulation accuracy.
A bit of EE humor.
