LOW NOISE INFRARED DETECTOR Grace Jung Travis Tanaka

LOW NOISE INFRARED DETECTOR Grace Jung, Travis Tanaka 1

• 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… 2

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. 3

IR EMITTER/DETECTOR CIRCUIT 4

PARTS LIST • Switch Parts • 4066 Analog Switch • Inverter • IR Detector/Emitter • LTR 301 IR Phototransistor • 270Ω 270 • LTE 302 IR Emitter • 100Ω 100 • 3 x 1 µF • 10Ω • 10 MΩ • 100 kΩ • 2 x LM 411 opamp • 10 kΩ • DC Power Supply • 1 kΩ • Oscilloscope 5

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 MRD 3051 phototransistor. 6

WHAT WE DID (2) Photodiode Input Chopper Circuit Output 7

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. 1 m. V vs MRD 3051 output of ~10 m. V 8

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 MRD 3051 phototransistor • To do (before final): • Implement IR devices • Fix saturation issues 9