noise experiment

Noise ExperimentsRay

Oct 13th, 2015

Preamp Analysis frequency domain

• Procedure:

1. Set its gain to 500V/V, input to gnd

2. Change the cutoff frequency of low-pass filter in preamp to see its output spectrum

• Observations:

1. Independent of the cutoff frequency, the high frequency thermal noise is always around -81dBVrms

2. When the cutoff frequency is between 1KHz to 10KHz, there are two plateaus with the second one as -81dBVrms

Preamp Analysis frequency domain cont.

• Conclusions:

1. Since the thermal noise in the first plateau is from the preamp input while the second is from preamp itself, we need to adjust the cutoff frequency to make the first plateau appear.

2. Also, we need the first plateau to be as long as possible to get rid of the roll-off effect from either flicker noise and preamp cutoff frequency.

1/f noise

thermal noise due to preamp input

thermal noise due to preamp

fL

Noise Analysis frequency domain

• Measurement Setup:

A

To Spectrum Analyzer

Preamp

1Mohm

VGS


RD

VGS

Weak Inversion Condition


• Setup detail:

1. No pole introduced in preamp

2. Device works in room temperature 73F

3. VGS=0.4V

Pole (detector induced*)

Noise Analysis Integration Method

Pole in preamp: 10Hz

1/f noise dominant


Pole in preamp: 10KHz

thermal noise dominant

Rload=1Kohm


Region 1

Region 2


• Region 1:

1. noise highly depends on the temperature

2. This temperature dependence is from the channel noise

• Region 2: noise is almost independent of the temperature

This happens because RD sits outside oven.

• No matter what is the reason, measuring temperature from 73F to 83F can tell us the channel noise dependence on the temperature

Noise Analysis vs Temperature frequency domain T=73F(296K)

• After averaging using two frequencies and five resetting, -55.023 dBVrms noise power spectrum density is derived and it equals to 3.146uV/sqrt(Hz).

• Since preamp gain is 500V/V, the equivalent noise spectrum density from the detector is 3.146u/sqrt(500), which is 0.1407uV/sqrt(Hz)

fL = 56.5KHz

Noise Analysis vs Temperature frequency domain T=83F(301.5K)



fL = 47.616KHz

Noise Analysis vs Temperature frequency domain T=93F(307K)



fL = 45.4KHz

Noise actually drops in this temperature

Noise Analysis vs Temperature frequency domain theoretic result

Channel Noise

Loading resistance noise

Frequency domain experiment result:

Noise Analysis vs Temperature frequency domain theoretic result

Channel Noise Weak inversion approximation

Loading resistance noise

Flicker Noise

Channel Noise strong inversion approximationFrequency domain experiment result:

noise experiment

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