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CAD For Noise Analysis

CAD For Noise Analysis. SPICE contains built-in models for passive elements, semiconductor devices …etc. by including control lines in an input file, SPICE can be made to perform various analyses of a circuit including noise analysis.

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CAD For Noise Analysis

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  1. CAD For Noise Analysis

  2. SPICE contains built-in models for passive elements, semiconductor devices …etc. by including control lines in an input file, SPICE can be made to perform various analyses of a circuit including noise analysis. • Noise analysis is performed in SPICE by using .NOISE statement in the input control file. • SPICE calculates shot noise and thermal noise for the circuit. Amplifier Noise Sources • For modeling purposes it is advantageous to lump all the noise produced by an amplifier or other functional block into 2 noise sources En and In as shown: • There are several ways to implement this type of an amplifier model in SPICE. The easiest way is to use 2 resistors as noise sources and reflect their noises to the appropriate nodes using dependent voltage and current sources. • Diodes can also be used as sources of shot noise and flicker noise and reflect their noises to the appropriated nodes in the circuit.

  3. Resistor Modeling Approach • SPICE calculates the thermal noise current in a resistor according to • Example: • Create En and In of and 10 respectively • We create 2 thermal noise current standards of 1 by using 2 resistors of value • 2 separate sources are necessary since it is normally assumed that the En and In amplifier noise sources are uncorrelated. • Polarity does not matter for any of the sources because noise is a squared quantity. The multipliers needed for the H and F sources are respectively • The SPICE codes are: RNE 100 0 16.5k; • VESEN 100 0 DC 0; HEN 1 3 VESEN 3k; • RNI 200 0 16.56 k; VISEN 200 0 DC 0; • FIN 2 3 VISEN 10

  4. If we desire to include the amplifier’s input impedance into our noise model, an extra noise will be unintentionally introduced through the resistive component of the input impedance. Modeling 1/f Noise • SPICE calculates the noise current in a diode according to • Example: Model En noise of 20 nV/Hz1/2 with a noise corner frequency fnce = 200 Hz and In noise of 0.5 pA/Hz1/2 with a noise corner frequency fnci = 500 Hz in each diode • The dc diode current is calculated according to • Next the flicker noise term is set equal to the 1-pA/Hz1/2 reference noise current at the fnc frequencies. For the Ensource with AF =1, KF is calculated by equating the two right-hand terms. Thus • Similarly KF for In is

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