Noise Analysis

The .NOISE statement is used to calculate noise contribution from each device and to perform an RMS sum at one output node.

*Entry*	*Description*
Output Variables	The list of voltages or currents for which total noise is generated and written to the .out file.
Source Variable	An independent source to which input noise is referred.
Start Frequency	The minimum frequency for the analysis.
End Frequency	The maximum frequency for the analysis.
Number of Points	Specifies the number of points per decade, octave or across the whole linear range.
Step Type	Dictates how DR. SPICE calculates the interval between the start and stop frequencies. The choices are Decade, Octave and Linear.
Print Summary Points	Controls the frequency interval at which DR. SPICE prints Noise Spectral Density and Integrated Noise curves to the .out file.
Title	Tile which will appear within the Simulation menu.

The Noise Analysis dialog box is analogous to the Spice3 .NOISE analysis command found in the circuit file. The syntax is:

.NOISE V(OUTPUT <, REF>) SRC {DEC/LIN/OCT} PTS
+ FSTART FSTOP <PTS_PER-SUMMARY>

DR. SPICE also accepts the SPICE2 format as input for noise analysis. The SPICE2 syntax is:

.NOISE V(<node>[,<node>]) <name> [(interval) value]

Examples:

.NOISE V(10) VCC 2
.NOISE V(1,2) VS
.NOISE V(10) IS

NOTE: In the SPICE2 format, .NOISE performs noise analysis over the frequency range specified in the AC analysis; therefore, an AC analysis is required when doing noise analysis. The AC analysis requires the existence of a .AC statement.

SPICE3 general format:

.NOISE V(OUTPUT <, REF>) SRC {DEC/LIN/OCT} PTS  + FSTART FSTOP <PTS_PER-SUMMARY>

The following list describes each abbreviation:

V(<node> [, <node>]) = output voltage. It has one of two forms: V(5), the voltage at an output node, or V(4,5), the output voltage across two nodes.
<name> = independent voltage or current source at which the equivalent input noise is calculated. It is not itself a noise generator, but only a place at which to calculate the equivalent input noise.
SRC = source (voltage or current)
DEC = decade variation
LIN = linear variation
OCT = octave variation
PTS = number of points specified
FSTART = starting frequency
FSTOP = final frequency

Example:

.NOISE V(2) VIN  DEC 4 10 100K 5

Output:

For CSDF output, look in the .txt file. The values read as Volts.

The .out file has the detailed tables with units of V²/Hz or A²/Hz depending on whether voltage or current noise is being measured:

V(INOISE):	Equivalent input noise at VIN
V(ONOISE):	RMS noise at node V(2)
V(os.device_param):	RMS noise at node V(2), and is the contribution from ’device_param’

If you are using Interactive Mode, there is another type of data available-the integration of the above waveform over frequencies. The results are in units V² or A ².

Noise Analysis Example

Input File, noise.cir:

* Project NOISE R1 VIN VCENT 1K R2 FOUT 0 2K C1 VCENT 0 239PF C2 FOUT 0 80PF L1 VCENT FOUT 212U VIN VIN 0 AC 1 0 Q1 AMP1 FOUT N163 Q2N3903 R3 N186 AMP1 2K R4 N163 0 1K V180 N186 0 DC 15V R5 N186 FOUT 2K * Note: * if SPICE2 format is being used * a .AC command is required to do .NOISE *.AC DEC 10 1KHZ 10MEGHZ *.NOISE V([FOUT]) VIN 10 * If you specify Frequency information on the * .NOISE line (DEC 50 10Hz 10MEGHz), then a .AC * Command is not required to do .NOISE .NOISE V([FOUT]) VIN DEC 50 10Hz 10MEGHz .PROBE/CSDF V([AMP1]) .PROBE/CSDF V([VCENT]) .PROBE/CSDF V([FOUT]) .OPTIONS ACCT NODE LIST * .model q2n3903 NPN( is = 2.96568e-15 va = 40 tf = 6.36943e-10 + ne = 1.2851 ise = 2.14091e-14 bf = 100.625 ikf = 0.05 + mje = 0.345335 cje = 4.38552e-12 mjc = 0.286574 cjc = 3.62782e-12) * .END

Output File (Partial), noise.out:

******************** Circuit: * Project NOISE ***************** ********** Run on Apr 12 1994 at 12:30:16 ******************** ************Noise Spectral Density Curves - (V^2 or A^2)/HzTEMPERATURE = 27.000 DEG C ****************************************** frequency v(inoise) v(onoise) v(os.q1) 1.0000e+01 5.5111e-17 1.3438e-17 5.3524e-18 1.0471e+01 5.5111e-17 1.3438e-17 5.3524e-18 1.0965e+01 5.5111e-17 1.3438e-17 5.3524e-18 1.1482e+01 5.5111e-17 1.3438e-17 5.3524e-18

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