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Guideline
0.3 Management:
Using a non-inverting amplifier circuit, train following things to student,
and have discussions with students




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Show how to use oscilloscope (how to read voltage, frequency etc)
Show how to use oscillator (different input wave, frequency, and amplitude)
Show how to read resister using different colors (4 bands, 5 bands)
Show how the wire is configured in the board
How to avoid damaging circuit?
o Don’t put any power line to oscillator
o Don’t put wrong power line to chip
o Turn off power first before you insert the chip to the circuit, or before you
take out the chip from the circuit.
 How to build a safe circuit
o Test the chip first before putting it into board
o Don’t turn on the power of the circuit board until you build the circuit
o Take advantage of four vertical lanes in the circuit diagram. (ex, ground
line, input line Vin etc)
o Take advantage of different colors of wire. (ex, ground line for brown
color, green line for input, red line for output etc). This will save a lots of
time for you when students ask you to check his/her circuit.
o Connect input oscillator at the end after you make sure there is no current
moving to the input oscillator.
 How to check, if it doesn’t work
o If you see something unexpected output, Vout
 Check the power of the circuit: many students forget to turn on the
power of the board.
 Check the input, Vin signal is correct and reasonable (suitable
frequency, and suitable amplitude not to be saturated) against
expected gain.
 Check the oscilloscope is in the proper mode for operation (not in
DC mode, timing etc)
 Check the +/-15 V power lines are connected. Especially, +15 V to
pin #7 tends to be connected to pin #8 by accident.
 Check other resisters/capacitors are properly connected.
 If it still doesn’t work, it may not be easy to find the problem. You
can look at few other things.
 If virtual ground exist, check the voltage is zero
 Suspect the chip
 Suspect wrong resister/capacitor
 Suspect broken line in the circuit board
 No luck so far: call other demonstrator or Un-ki
o Once you find the solution, don’t provide the solution immediately, but
lead student to come to that solution.
2.3 Inverting amplifier and summer
Inverting amplifier:
Expected gain: G = - R2/R1 with 180 phase difference
Summer: Vout = V1 + V2
Tips:
 Don’t use too small value of the gain. Remember the expected gain comes,
assuming beta (=R1/R2)*G(intrinsic) is very large.
 Don’t use too large value of the gain. Output will be saturated. Output signal
cannot be larger than the power supplier voltage, 15 V. So suitable choice will be
0.5 – 100 for gain. Resisters: 1K – 1M ohm.
 Gain should be constant at low frequency, but gain drops and output shape is
changed as the frequency is increased, depending on the gain.
 If output is in phase with input signal, check that +15V is connected pin 7 (not
pin 8)
2.4 Integrator
circuit diagram: replace R2 with capacitor
Gain (=Vout/Vin) = -Z2/Z1 = -1/jwC/R1 = -1/jwRC
Vout = V0 exp (jwt) = - (1/RC) integral (Vin)
Tips




Use the simplest input wave (square wave). Output should be the triangle wave.
You may not see the clean triangle wave, without adding a large resister (1M
ohm) in parallel across the capacitor. This resister will spit the current, not
saturating capacitor. Use R1=200K, C=10nF
Don’t use too small value of the gain. Remember the expected gain only depends
on external circuit components, assuming beta (=R1/R2)*G(intrinsic) is very
large.
Don’t use too large value of the gain. Output will be saturated. Output signal
cannot be larger than the power supplier voltage, 15 V. So suitable choice will be
0.5 – 100 for gain. Resisters: 1K – 1M ohm.
2.5 Phase shifter
ZC
VIN
R2  ZC
VIN  V V  VOUT

 V  (VIN  VOUT ) / 2
R1
R1
V  V according to Golden rule
V 
V 
VOUT
VIN
ZC
VIN  (VIN  VOUT ) / 2
R2  ZC
Z  R2
 C
, where Z C  1 / jwC
Z C  R2
VOUT 1  jwR2C 1  (wR2C)2  2 jwR2C


VIN
1  jwR2C
1  (wR2C)2
tan 1   2wR2C / {(wR2C)2  1}  1.732
For 1kHz frequency,
1  1  1.732 2
RC 
 1.732 / (w  6.28 *1.000)  2.758  10 4
1.732w
2.6
In the real world: gain limitation
A realistic OP amplifier don’t have an infinite gain, and it’s gain
drops at high frequency, and output response is not instantaneous.
Slew rate: the rate at which the output voltage can change: V/t,
typically, 106V/s
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Gain: Large bandwidth with lower gain:
Don’t saturate output voltage using higher input voltage
and higher gain
Go
QuickTime™ and a
F (Uncompressed) decompressor
re needed to see this picture.
G
Bandwidth
-
2.7
Output impedance
Output impedance is very small, ~100 ohm. With external resister
r, Vout will drop by r/(r+R). Use a small resister. It would be very
hard to see any chance with large value of the resister (>1k ohm).
3.2 Schmitt trigger
Make sure that student draw output very carefully in their logbook,
especially threshold region. If there is any student, you can guide
them to use two oscillators plus summer circuit (two sine waves
with small and large amplitudes). This will produce a noisy signal.
+15
V(H)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
V(L)
-15V
t
t1 t2
3.3
Astable multivibrator
Vout: oscillating square wave
Vout signal goes to V+ via a positive feedback, and Vout signal
also goes to V- via a negative feedback. Vout depends on the
comparison of V+ (=Vref) and V- (Vramp).
If V+ > V-, Vout will have a saturated output, +15V.
Then, V+ has a positive voltage
(=4.7/(47+4.7)Vout=0.9*15V=1.36V)
and the capacitor will be positively charged up. Once V- exceeds
V+, then Vout will be immediately -15V, then the capacitor will
start to discharge until V- is below V+. This will produce an
oscillation. Oscillation frequency will be determined by the
capacitor and 10Kohm. (positive
feedback is immediate, whereas
QuickTime™ and a
decompressor
negative feedbackTIFF
is (Uncompressed)
delayed by ~RC
amount)
are needed to see this picture.
3.4
Wien bridege oscillator
R2
Z2
VOUT , V 
VOUT
R1  R2
Z1  Z 2
R / jwC
1  jwCR
Z2 
, Z1 
R  1 / jwC
jwC
V 
jwCR 2
V 
VOUT  V ,
2
1  (wCR)  3 jwCR
Thus, imaginary component of V+ should be zero
So, w=1/RC
And, V =0.33RVOUT , V- will be set to V+ using a light bulb.
4.3 Flash ADC
LM311 CHIP WILL BE USED, NOT 741 CHIP: EMPHASIZE TO STUDENTS
THAT THIS CHIP HAS DIFFENT PIN ASSIGNMENTS FOR POWER AND
OUTPUT.
See how we setup a voltage divider to make 3V, 2V, and 1V for C3, C2, and C1
respectively.
+Vcc should be +15 V, and –Vcc should be -15V
In this circuit, there is a high risk to burn the oscillator or circuit, based on last
year’s experience, because there are so many wire connections and power lines for
this chip are changed, compared to the previous experiment. Absolutely necessary
to check Vin wire line using oscilloscope, because they connect Vin wire to the
oscillator.
How to setup above encoder?
A  C2, B  C3  C2   C1
 : XOR gate (chip #7486)
or
A  C2, B  C3  C2   C1
 : XNOR gate
Once students setup their ADC, demonstrator needs to confirm their circuit design and
output. Because output is LED signal, practically it is not possible whether they have
built ADC properly or not.
It is also good to ask them draw Vin and A channel together using oscilloscope for a
triangle wave (with 4V amplitude). Vin and B channel too.