system level modelling presentation

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    Modeling Analog Non linearitiesfor Delta Sigma Modulator

    Behavioral system level understanding &

    simulations

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    Common Biomedical Signals

    Low frequency and low amplitude signals

    Detection difficult as coupled with flicker noise, Common mode noise and electrode offset

    voltage.

    Electrodes eliminate common mode gain.

    DC component eliminated - choppers

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    Bio Signal sensing and processing system

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    Input Signal BW=05 Hz to 1KHz

    OSR= 1024

    Order of Modulator= 2

    LP or BP= LP

    DR= 70dB

    ENOB= 18

    QUANTIZATION BITS=1

    System Level Specifications

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    For OSR=1024

    L=2B=1

    DR(dB)=115

    ENOB=18

    Performance Parameters

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    The calculation of these coefficients is based

    on the fact that the pulse response of filter is

    weighted response of the all the pulses

    generated by each feedback in DSM

    architecture. This yields us with a system of

    linear equations ..

    The output matrix

    System of linear

    equations

    Solution to the system of linear

    equations gives us the required

    coefficients

    Calculating coefficients

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    non-idealities

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    Variations from ideal clock edges vary the feedback pulse length

    Clock jitter causes error sequence in CT :

    e(z) = { y(n) y(n-1) } * bn /Ts

    Adds additional noise in DAC through feedback which is NOT shaped by loop filter

    Simulation show NRZ codes & multi bit quantization are less sensitive to jitter

    Modeling Clock Jitter

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    Modeling Integrator Noise

    thermal noise - caused by random fluctuations of carriers due to thermal energy

    white spectrum and wide band, limited the BW of the operational amplifiers

    Flicker noise - 1/f noise decrease with frequency increase

    Time domain emulated sources of both noises are sum of N sine waves with randomphase

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    Ideally infinite but actually limited by circuit constraints & op amp open loop gain

    pole of integrator is pushed from dc to a / (Ao + 1)

    TF of finite GBW & gain is:

    Ideal TF is replaced by this eq. in simulink model

    Modeling Finite Gain & GBW

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    Modeling Slew Rate

    Rate at which the output changes with the change in input