PHYS 253 – Introduction to Instrument Design summer 2009 www

PHYS 253 – Introduction to Instrument Design
www.engphys.ubc.ca/phys253
summer 2009
Lab 2 – Analog Circuits
Objectives: To amplify a signal from an IR (infrared) receiver, change its DC level and
amplitude, filter it to remove unwanted noise, and convert its amplitude to a DC signal (peak
detect). These functions are the core elements of an infra-red homing system.
Pre-Lab
Derive the gain functions for the inverting, non-inverting, and differential amplifier
configurations shown below.
2. Draw a frequency response plot for the passive low pass filter shown in Fig. 1.5
3. Derive a transfer function for the active bandpass filter in Fig. 1.6
4. Read data sheets on OP805, TL082.
1.
Operational Amplifiers
The Inverting Amplifier
In this configuration, the input signal is connected to the inverting (negative) terminal, while the
noninverting (positive) terminal is connected to ground.
RF
Vcc
RS
+
U1
UA741
TL082
Vo
+
-
Vs
Vee
Figure 1.1
The Noninverting Amplifier
To avoid the negative gain present in the inverting amplifier, the noninverting amplifier
configuration is used. Just as the name indicates, the input signal is connected to the
noninverting terminal.
RF
Vcc
RS
U1
UA741
TL082
+
Vo
R
+
Vs
Vee
-
Figure 1.2
The Differential Amplifier
This configuration is used in situations where the difference between two signals needs to be
amplified. The basic differential amplifier circuit is shown below.
R2
Vcc
U1
R1
UA741
TL082
+
Vo
+
R1
+
V2
V1
R2
Vee
-
-
Figure 1.3
Filters
High Pass Filters (passive)
C
Vo
n
R
Figure 1.4
Low Pass Filter (passive)
R
Vo
n
C
Figure 1.5
Active first order band pass filter
R1
C1
R2
C2
U1
TL082
Figure 1.6
Peak Detector
This circuit is capable of tracking the amplitude of a sinusoid with a response time constant of
R1C1, where R1C1 determines the response time of the peak tracking.
Vcc
+12V
Vcc
+12V
U1
TL082
+
U2
TL082
D2
1N914
+
Vin
Vout
C1
Vee
-12V
R1
Vee
-12V
Figure 1.7
Lab 2
Assignment
1. Wire up a phototransistor (OP 805 or OP830) on your protoboard as per test circuit
shown in data sheet. Make sure you do not exceed max. voltage ratings for these devices.
2. Expose the phototransistor to a flashing IR source and measure output waveform on
scope. Note at this time the amplitude and frequency response of the phototransistor.
(optional but recommended) There are six IR sources in the classroom set to produce 1
kHz and 10 kHz sine waves and square wave output. It is also advantageous to hook up a
signal generator to drive an IR LED directly, which allows you to vary the frequency
continuously and see the frequency response of your system.
4.5V
Vin
500 ohm
0.5V
Note: The phototransistor has a base lead to allow the transistor to be turned on electrically
rather than with light. You do not need to wire the base to anything – if you do run current
into the base, it will tend to turn on the transistor just like light falling on it would.
3. Design and wire up an amplifier or sets of amplifiers to amplify the output waveform.
Keep in mind the gain-bandwidth product of the TL-082 op-amps, and use multiple
stages if necessary to achieve your desired gain without losing frequency response.
Remember to block the DC component of the signal before amplifying.
4. Design and build a band pass filter to detect a 10kHz IR sine or square signal and reject
noise at other frequencies. Test the amount of rejection you have achieved by exposing
your circuit to a 1 kHz IR sine wave.
5. Design and build a peak detector to produce a DC analog signal proportional to the
amplitude of the detected IR signal.
Make sure the output of your peak detector swings between 0-5V to match the input range of
the TINAH Board.
DO NOT TAKE APART YOUR CIRCUIT AS YOU WILL NEED IT NEXT WEEK.
Milestone:
Show your TA that your circuit produces a DC signal proportional to the amplitude (or
distance) of the IR beacon.
Note: keep careful notes on all your circuits and the problems / solutions you have
encountered. You will need all this for the IR detector on your robot.
Your final circuit should look something like this:
Photo
transistor
Amplifier
Filter
Peak detector