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April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Recap•RTOS •Debugging/verification
Lab 4 Application of RTOS
• Input sound, analog filter • Digital filter, FFT• Display amplitude versus freq on the oLED
Noise Reduction
-2048
-1536
-1024
-512
0
512
1024
1536
2048
0 1000 2000 3000 4000 5000 6000 7000
Time
Ou
tpu
t
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Objectives
• Analog circuit design with single supply – MAX494CPD/TLC2274ACN rail to rail op amp
• Instrumentation amps (EE445L) – INA122
• Noise measurements and reduction
• Electret microphones
• IR distance sensor
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Convert to single supply• Vcc = 3.3V, start with design using +Vs -Vs• Assume ADC range is 0 to Vmax (0 to 3V) • Add an analog reference, Vref = ½ Vmax• Map
-Vs (-12) to digital ground
Analog ground to Vref reference
+Vs (+12) to Vcc supply
Reference EE345L book, chapter 5
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Inverting amp
yVI
I Vx
y
x
R1 R2
R3
Vin
R1
R2 VinV = -out
R =3 R +1 R2
R *1 R2
I2I in
+Vs
-Vs
0.1F
0.1F
Use a rail-to-rail opamp and map-Vs to digital groundAnalog ground to Vref reference+Vs to Vcc supply
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Instrumentation amp
• Necessary conditions (must be true)– Differential input
• Motivation (at least one must be true)– Large gain– Large CMRR– Low noise– Small package– Large input impedance
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
INA122
Final exam 2006, Q5
Vout = Gain*(V1-V2) + Vpin5
V1
V2
Vout
Vpin5
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Magnetic field noise
I1
Vs
ACpower
V1
Mutual inductance
S
Vs
V1
V = KBSm
Im
Motor Ourinstrument
Magnetic field
How do you reduce S?
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Electric field noise
Electric field
I1
Vs
ACpower
V1
Motor
Vs
V1
Stray capacitance
Id
Ourinstrument
How do you reduce C?
C
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Measure noise
Voltage
Time
Peak-to-
peak
White or 1/f noise Voltage
Time
Peak-to-
peak
Periodic noise
• DVM (AC mode)
• Oscilloscope (line trigger)
• Spectrum analyzer1000
100
10
11 10 100 1k 10k 100k
VoltageNoise
Frequency (Hz)
60Hz noise
1/f noisewhite noise
bandwidth limits
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Reduce noise
1) Reducing noise from the source– enclose noisy sources in a grounded metal
box– filter noisy signals– limit the rise/fall times of noisy signals. – limiting the dI/dt in the coil.
Noisy Less noisy
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Reduce noise
2) limiting the coupling between the noise source and your instrument.
– Maximize the distance from source to instrument – Cables with noisy signals should be twisted together, – Cables should also be shielded. – For high frequency signals, use coaxial – Reduce the length of a cable– Place the delicate electronics in a grounded case– Optical or transformer isolation circuits
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Reduce noise
2) limiting the coupling between the noise source and your instrument.
Shielded cable
Twisted wires
RoutZin
Transducer Instrument
Shielded cable
Twisted wires
RoutZin
Instrument Instrument
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Reduce noise
– 3) reduce noise at the receiver. – bandwidth should be as small as possible. – add frequency-reject digital filters– use power supply decoupling capacitors on each – twisted wires then Id1 should equal Id2. – V1-V2 = Rs1 Id1 - Rs2 Id2.
Id1
Vm
Vs
Rm
Rs1
Rs2
Rin1Rin2
Rdiff
Amp
Id2
V1
V2
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Typical cross section of an ECM
• JFET buffer
• Phantom Biasing
Data sheet says 2k
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
Electret interface
Bias
HPF
Offset for single supply operation Balance Z to subtract bias current
LPF
LPF fc = 1/(2R13*C6)
HPF fc = 1/(2R9||R10)*C5)Gain = 1+R13/R12
Use max494
Show Measurements
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
• Noiseo DVMo AC mode on scopeo Spectrum analyzer
• Signalo Peak to peako Spectrum
Sharp GP2Y0A21YK
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
• You will need 5V to power IR sensor • Needs analog LPF• Reduces noise• Analog input protection• Needs digital median filter• Needs 10 F or larger +5V to gnd cap
for each sensor
Sharp GP2Y0A21YK
April 18, 2023 Jonathan Valvano EE445M/EE380L.6
d (cm) 1/d ADC10 0.100 70315 0.067 48420 0.050 38030 0.033 260
Calibration
ADC = 6706.7/d + 39.643
R2 = 0.9988
0100200300400500600700800
0.000 0.020 0.040 0.060 0.080 0.100 0.120
1/d (1/cm)
10-
bit
AD
C