Electronics > Projects, Designs, and Technical Stuff
What is your favorite most versatile op-amp?
Zero999:
--- Quote from: MasterT on June 09, 2019, 01:47:47 pm ---From NE5532 DS TI : Equivalent Input Noise Voltage: 5 nV/√Hz Typ at 1 kHz
OnSemi: Input Noise Voltage: 5.0 nVń Ǹ Hz (Typical)
LM4562 TI : Input Noise Density: 2.7nV/√Hz (typ)
--- End quote ---
You've misread my post. I know the voltage noise is lower. I was taking about the current noise, which is higher, than the NE5532 at 1kHz. The LM4562 has 1.6pA/√Hz vs only 0.7pA/√Hz for the NE5532. If the impedance seen by the input is greater than about 2k925, the LM4562 will be more noisy, than the NE5532.
The current and voltage noise densities add at the op-amp inputs. The current noise forms a voltage noise source, when if flows through the resistance, connected to the input.
VN_TOT = √(VN2+(IN×ZIN)2)
So if you have an inverting amplifier.
Rin = 10k
IIN = 0.7pA√Hz
VN = 5nV/√Hz
VN_TOT = √(10k×0.7p)2+5n2 = 8.6nV/√Hz
If Rf = 100k then the gain will be 100 so the output voltage noise will be 860nV/√Hz.
nemail2:
OPA2197 it is, for me...
MasterT:
--- Quote from: Zero999 on June 09, 2019, 03:51:02 pm ---You've misread my post. I know the voltage noise is lower. I was taking about the current noise, which is higher, than the NE5532 at 1kHz. The LM4562 has 1.6pA/√Hz vs only 0.7pA/√Hz for the NE5532. If the impedance seen by the input is greater than about 2k925, the LM4562 will be more noisy, than the NE5532.
--- End quote ---
I see, the point of this thread is to define a priority list of the OPA's parameters. Since there is no perfection in this world, no OPA that would satisfy all requirements. Current noise is the last line of all spec I'd care about.
Voltage offset is close to the middle of the list. Its' easy to fix in hardware or software. The THD is the most important, difficult to straight up and it's directly limit accuracy of the circuits. DC accuracy is no exception, basically THD is equivalent to INL / DNL in the ADC-DAC specification. Long time THD is associated with audio, or AC in general, but IMHO it's a big mistake to use LM358 at the front end of the anything with >12-bits resolution. And input offset is not an issue.
exe:
--- Quote from: MasterT on June 09, 2019, 04:19:01 pm ---The THD is the most important, difficult to straight up and it's directly limit accuracy of the circuits. DC accuracy is no exception, basically THD is equivalent to INL / DNL in the ADC-DAC specification. Long time THD is associated with audio, or AC in general, but IMHO it's a big mistake to use LM358 at the front end of the anything with >12-bits resolution. And input offset is not an issue.
--- End quote ---
Isn't THD frequency-dependant? If so, can lm358 still be good for low-frequency signals?
As for offset, why do you say it's not an issue? If DC accuracy is required, it is an issue.
SiliconWizard:
One thing to note about the NE5532 is that (at least in the TI datasheet for the NE5532 that I have) there is no figure to be seen regarding distortion. Did I stupidly miss it? Does anyone have a datasheet stating distortion? And if we're going to use NE5532's made by TI, how are we going to know what to expect in terms of distortion?
I've used the LME49720 with very good results for current-to-voltage output stages for audio DACs.
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