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Interactive Design Tools: Operational Amplifiers : OpAmp Error Budget Calculator

An online tool to illustrate range, gain and accuracy issues with OpAmps. Select an amplifier from the pull down list, or manually enter parameters.

Instructions | Troubleshooting | Related Information
Topology Positive Supply  
Schematic
Ideal Gain
Ideal Node Voltages
VIN(+)
V
VREF / VIN-
RS+
K ohms
RS-
K ohms
RG
K ohms
RG2
K ohms
RF
K ohms
RF2
K ohms
Negative Supply  
RX
K ohms
RL
K ohms

 
Application Parameters

Operating Temp., TA °C
Supply Variability
(ripple+load reg.)
%

Error Source Specification Approx. Calculation Absolute
Error
Drift/Gain
Error
Resolution
Error

Resistor Tolerance %   ppm
Resistor Drift, TCR

Temp. difference, TDIFF

ppm / °C
°C
~ (1/2 : noninv) TCR × TDIFF   ppm
Nom. Open Loop Gain, AOL V/mV ppm
Min. Open Loop Gain V/mV   ppm

Input Offset Voltage, VOSI mV VOSI / (VIN-VREF)   ppm
Input Offset Voltage Drift, VOSI_TC µV / °C (2 : inv.) VOSI_TC × (TA-25) /
(VIN-VREF)
  ppm

Bias Current, IB
- Source Imbalance Error
nA ( IB / (VIN-VREF) ) ×
( RF||(RG+RS-) - (RG2+RS+) )
  ppm
Bias Current Drift, IB_TC
- Source Imbalance Drift
pA / °C ( IB_TC × (TA-25) / (VIN-VREF) ) ×
( RF||(RG+RS-) - (RG2+RS+) )
  ppm
Offset Current, IOS
- Source Imbalance Error +
  Source Resistance Error
nA ( IOS / (VIN-VREF) ) ×
( 3*(RF||(RG+RS-)) - (RG2+RS+) )/2
ppm
Offset Current Drift, IOS_TC
- Source Imbalance Drift +
  Source Resistance Drift
pA / °C ( IOS_TC × (TA-25) / (VIN-VREF) ) ×
( 3*(RF||(RG+RS-)) - (RG2+RS+) )/2
  ppm

Common Mode Rejection Ratio, CMRR dB (inv: (1+1/gain)×) 10 -CMRR/20 ×
| (V++V-)/2 - (VS++VS-)/2 | /
| VIN-VREF |
  ppm
Power Supply Rejection Ratio, PSRR dB (inv: (1+1/gain)×) 10 -PSRR/20 × ( | VS+-VS+nom | +
| VS--VS-nom | ) / | VIN-VREF |
ppm
10 -PSRR/20 × SUP-VAR ×
( VS+-VS- ) / | VIN-VREF |
  ppm

Noise BW 0.1 -
Hz
    ppm   
Voltage noise, VNW
nV/root-Hz
Corner freq   Hz
Current noise, INW
pA/root-Hz
Corner freq   Hz

Total resolution error   ppm
Total drift / gain error   ppm
Total absolute + drift + resolution error   ppm

Instructions

This calculator has two parts: an annotated schematic at top and a table of contributing error sources at bottom. Opamp parametric data is automatically entered in the appropriate fields of the bottom table, and default values for the application parameters have been assigned to the application-specific fields at top. All input data can be manually overridden, however output fields (surrounded by light gray) cannot be changed.

After entering data in a field, hit tab or click "Update" to compute derived values and see node voltages updated on the schematic. If the inputs are out of range an alert will appear. If the combination of inputs causes internal or external output limits to be exceeded, the problem node value will be highlighted in red and an "Out of Range!" message will appear. When this message is present, all node values should be considered invalid. Do not leave fields blank: if you see NaN (Not a Number), this means that insufficient data was entered to compute a value.

"Gain" and "RF" are computed automatically from one another, based on the value of "RG". The calculation is ideal and doesn't reflect RS, RX and RL, for example.

Equations listed in the "Calculation" column are approximate and reflect the worst case between the three buffer choices. Modifications to the equation for particular buffer types are indicated in (). For example (1/2 : noninv) means an additional factor of 1/2 should be used to compute this quantity for noninverting buffers.

Specs shown are worst-case for the selected part, if available, otherwise typical values are used. If no spec is available, "N/S" will appear in that field and an ideal spec (usually zero) will be used for the calculation. Please note that it is highly unlikely that all worst-case specs would ever be present at the same time in the same part. The designer should always refer to the appropriate datasheet and substitute numbers most appropriate to his/her application. All calculations are approximations with errors displayed and summed in absolute PPM, even though in some scenarios the actual values would be negative.


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Troubleshooting

No special issues are known to exist with this calculator at this time.

For further troubleshooting information, please visit our Interactive Tools troubleshooting page.


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Related Information

Amplifiers and Comparators

Amplifiers for Signal Conditioning (pdf, 407,203 bytes)


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