LOW NOISE INFRARED DETECTOR Grace Jung, Travis Tanaka 1

Goal: To detect and amplify a small IR DC signal through background.Goal: To detect and amplify a small IR DC signal through background. Problem: It is hard to build large gain DC Amplifiers with lowProblem: It is hard to build large gain DC Amplifiers with low Input Offset VoltageInput Offset Voltage 1/f Noise1/f Noise Solution…Solution… 2

CHOPPER AMPLIFIER 1949 – Edwin A. Goldberg designed chopper-stabilized amplifier1949 – 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.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 PartsSwitch Parts 4066 Analog Switch4066 Analog Switch InverterInverter IR Detector/EmitterIR Detector/Emitter LTR301 IR PhototransistorLTR301 IR Phototransistor LTE302 IR EmitterLTE302 IR Emitter 3x 13x 1 µF 10MΩ 100kΩ 10kΩ 1kΩ 270Ω 100Ω 10Ω 2x LM411 opamp DC Power Supply Oscilloscope 5

WHAT WE DID (1) Digikey shipping delays so we just got the parts yesterday evening.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.We built the circuit and substituted the IR emitter/detector pair for room lights and a MRD3051 phototransistor. 6

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

PLANS FOR FINAL PRESENTATION Swap in IR Emitter and ReceiverSwap in IR Emitter and Receiver Fix saturation issuesFix saturation issues The output is the same for the phototransistor covered or uncovered.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 ~10mVMight just be fixed by switching to IR parts since the IR output voltage is ~0.1mV vs MRD3051 output of ~10mV 8

SUMMARY Goal: Detect and amplify small IR signal through backgroundGoal: Detect and amplify small IR signal through background Plan: Use chopper amplifier to minimize noise while providing high gain Plan: Use chopper amplifier to minimize noise while providing high gain What we did:What we did: Built circuit with MRD3051 phototransistorBuilt circuit with MRD3051 phototransistor To do (before final):To do (before final): Implement IR devicesImplement IR devices Fix saturation issuesFix saturation issues 9