Lab # 5: Construction techniques Task 1: Construction

PHY 405: Electronics Lab
Lab # 5
Lab # 5: Construction techniques
In this lab you will learn some useful techniques for building opamp circuits.
Background preparation
• Analog Devices MT-100: prototyping techniques.
• Opamp imperfections: AOE, Section 4.4.1
Task 1: Construction
Construct the same final circuit as in Lab # 4, but do not use the solderless proto-board.
Use the following guidelines.
a) Construct your circuits by soldering components to the solderable breadboard. Lay
out your circuit neatly before you solder everything in. One option is to place your
components on the top side of the board, and attach jumper wires on the under
side. However, feel free to develop a technique that works for you.
b) Use wires with different jacket colours for the power supply rails, ground, and signal
connections. Keep all the wires as short as possible. Twist wire pairs together,
especially signal connections and their returns, for improved shielding. Avoid
criss-crossing signal connections. A rat’s nest of wires is guaranteed to have lots of
pickup (and will be impossible to debug).
c) Wire the power connections from the circuit board directly into the outlet screws
on the DC power supply.
d) Bypass the power supply at each opamp: connect decoupling capacitors (∼ 0.1 µF)
close to the power supply pins of the opamps, as shown in Figure 1.
e) Connect BNC panel-mount jacks with twisted wire pairs to the inputs and outputs
of the amplifiers. (Observe the demo circuit in the lab to get an idea of how to do
this.) This will allow you to apply and measure voltages at various nodes in the
circuit using shielded coaxial cables.
f) You may find that some opamp chips have a DC error: they may display a DC voltage
at the output, even if the voltage applied to the input is zero. This is called a
input offset voltage, VOS . You can trim these offsets away: use a 25 k trimming
potentiometer (“trim pot”) to adjust the offset voltage, as shown in Figure 2. Verify
that this works by examining the output of your opamp circuit on an oscilloscope.
(2 hours)
In your report, demonstrate that you have constructed a well-behaved circuit.
Comment on the value that you measured for the Boltzmann constant using this
PHY 405: Electronics Lab
Lab # 5
VFigure 1: Power supply decoupling with bypass capacitors. Most schematics do not
explicitly indicate these, but you should always decouple the power supplies on your
Figure 2: Offset adjustment with a 25k trimpot (Figure 55 in the LF356 opamp