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The FAQ states: >"Q: What are some of the issues associated with analog computation? A: They are similar to the ones that are of concern whenever analog funct

The FAQ states: >"Q: What are some of the issues associated with analog computation? A: They are similar to the ones that are of concern whenever analog functions (op amps and more) are used for signal processing or signal conditioning. These include linearity, offset, temperature-related drift, aging, and bandwidth." I understand bandwidth but could someone elaborate in lay terms what these other "concerns" are in analog circuits? Specifically what are linearity and drift?

detaro 8y ago
Linearity: you expect a circuit to e.g. always multiply an input with 2x. Turns out it doesn't, it does so close to e.g. 0, but multiplies by less or more at higher values. Somewhat generalized, for other components with other curves of behavior, they also don't stick perfectly to the mathematical model, especially when the environment changes. Which leads us to Drift: temperature changes, behavior of component changes (e.g. resistors change slightly in resistance, circuits to generate precise voltages produce slightly different voltages, oscillators change in frequency). E.g. precision frequency sources often have a heating element to keep their core oscillator at a stable frequency, audio devices thermally couple two components of which the ratio is important, so the changes cancel out as much as possible, ...
pjc50 8y ago
Linearity: if a system is linear you can draw a nice straight line on an X-Y plot of input vs output. Nonlinearity is a measure of how much it deviates from that line. Drift: component values are not fixed! Most vary slightly with temperature, and capacitors change value over time too. Can be seen in any kind of old equipment which needs to "warm up".
- bogomipz 8y ago
  Thanks for the wonderful and detailed responses. I really appreciate it. One follow up - is it accurate to say that linearity and drift are always related then?
  - pjc50 8y ago
    Not really, they're separate parameters. Things like crystals and diodes are subject to drift without being linear at all. And ADC/DAC designers worry about linearity a lot while not being concerned about drift, because that gets outsourced to the reference voltage.
Kirby64 8y ago
Linearity and drift already covered by the other the other folks... Offset: When something is supposed to read a specific value (usually voltage), what is it actually reading? Most op-amps (configured as buffers) won't actually read 0V if 0V is applied. Usually this offset is super small (10s of mV, or even way less) in modern op-amps. Sometimes it's offset current. Many op-amps specify both current and voltage offset. Temperature-related drift: This is component value change specifically related to temperature. Multi-layer ceramic capacitors are especially susceptible to this. A 'good' MLCC might 'only' drift +/-20% across temperature Aging: As a component ages, how does its value change? Electrolytic capacitors have this problem. If you've ever heard of people talking about replacing capacitors on old TVs or what-not, it's almost always those caps. The paste in the electrolytic caps dries out and affects the value of the capacitor. Once this reaches a certain point, the circuit won't work anymore. Note I provided specified examples for each of those problems, but they exist across pretty much every type of component to various degrees. For example, linearity can be a big issue on ceramic capacitors. Their values can change as much as 80% (yes, 80%) with applied voltage which can cause some really weird non-linear behavior to some circuits. Most modern silicon probably doesn't have many problems with aging unless it's driven to the ragged edge of its performance or there's an actual defect, since typically chips are qualified to run for a minimum of 100,000 hours. That being said, eventually it WILL fail if it's running constantly. Electromigration affects all silicon. By comparison, usually electrolytic capacitors you'll be lucky to get 10,000 hours out of them. Less the hotter they get and the more the voltage applied is.

detaro 8y ago

Linearity: you expect a circuit to e.g. always multiply an input with 2x. Turns out it doesn't, it does so close to e.g. 0, but multiplies by less or more at higher values. Somewhat generalized, for other components with other curves of behavior, they also don't stick perfectly to the mathematical model, especially when the environment changes. Which leads us to Drift: temperature changes, behavior of component changes (e.g. resistors change slightly in resistance, circuits to generate precise voltages produce slightly different voltages, oscillators change in frequency). E.g. precision frequency sources often have a heating element to keep their core oscillator at a stable frequency, audio devices thermally couple two components of which the ratio is important, so the changes cancel out as much as possible, ...

pjc50 8y ago

Linearity: if a system is linear you can draw a nice straight line on an X-Y plot of input vs output. Nonlinearity is a measure of how much it deviates from that line. Drift: component values are not fixed! Most vary slightly with temperature, and capacitors change value over time too. Can be seen in any kind of old equipment which needs to "warm up".

bogomipz 8y ago
Thanks for the wonderful and detailed responses. I really appreciate it. One follow up - is it accurate to say that linearity and drift are always related then?
- pjc50 8y ago
  Not really, they're separate parameters. Things like crystals and diodes are subject to drift without being linear at all. And ADC/DAC designers worry about linearity a lot while not being concerned about drift, because that gets outsourced to the reference voltage.

Kirby64 8y ago

Linearity and drift already covered by the other the other folks... Offset: When something is supposed to read a specific value (usually voltage), what is it actually reading? Most op-amps (configured as buffers) won't actually read 0V if 0V is applied. Usually this offset is super small (10s of mV, or even way less) in modern op-amps. Sometimes it's offset current. Many op-amps specify both current and voltage offset. Temperature-related drift: This is component value change specifically related to temperature. Multi-layer ceramic capacitors are especially susceptible to this. A 'good' MLCC might 'only' drift +/-20% across temperature Aging: As a component ages, how does its value change? Electrolytic capacitors have this problem. If you've ever heard of people talking about replacing capacitors on old TVs or what-not, it's almost always those caps. The paste in the electrolytic caps dries out and affects the value of the capacitor. Once this reaches a certain point, the circuit won't work anymore. Note I provided specified examples for each of those problems, but they exist across pretty much every type of component to various degrees. For example, linearity can be a big issue on ceramic capacitors. Their values can change as much as 80% (yes, 80%) with applied voltage which can cause some really weird non-linear behavior to some circuits. Most modern silicon probably doesn't have many problems with aging unless it's driven to the ragged edge of its performance or there's an actual defect, since typically chips are qualified to run for a minimum of 100,000 hours. That being said, eventually it WILL fail if it's running constantly. Electromigration affects all silicon. By comparison, usually electrolytic capacitors you'll be lucky to get 10,000 hours out of them. Less the hotter they get and the more the voltage applied is.