Download Low Noise Infrared Detector

LOW NOISE INFRARED
DETECTOR
Grace Jung, Travis Tanaka
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• Goal: To detect and amplify a small IR DC
signal through background.
• Problem: It is hard to build large gain DC
Amplifiers with low
• Input Offset Voltage
• 1/f Noise
• Solution…
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CHOPPER AMPLIFIER
• 1949 – Edwin A. Goldberg designed chopper-stabilized
amplifier
• Principle: The input DC signal is “chopped” and thus
converted to AC. Then the AC signal is amplified, and
these outputs are integrated back together to recover
the original signal.
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IR EMITTER/DETECTOR CIRCUIT
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PARTS LIST
• Switch Parts
• 4066 Analog Switch
• Inverter
• IR Detector/Emitter
• LTR301 IR Phototransistor
• 270Ω
• LTE302 IR Emitter
• 100Ω
• 3x 1 µF
• 10Ω
• 10MΩ
• 100kΩ
• 2x LM411 opamp
• 10kΩ
• DC Power Supply
• 1kΩ
• Oscilloscope
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WHAT WE DID (1)
• Digikey shipping delays so we just got the parts
yesterday evening.
• We built the circuit and substituted the IR
emitter/detector pair for room lights and a
MRD3051 phototransistor.
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WHAT WE DID (2)
Photodiode Input
Chopper Circuit Output
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PLANS FOR FINAL PRESENTATION
• Swap in IR Emitter and Receiver
• Fix saturation issues
• The output is the same for the phototransistor
covered or uncovered.
• Might just be fixed by switching to IR parts since the
IR output voltage is ~0.1mV vs MRD3051 output of
~10mV
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SUMMARY
• Goal: Detect and amplify small IR signal through background
• Plan: Use chopper amplifier to minimize noise while providing
high gain
• What we did:
• Built circuit with MRD3051 phototransistor
• To do (before final):
• Implement IR devices
• Fix saturation issues
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