Never tried an active notch. I don't believe them. It’s hard to imagine that an active notch can distort less than passive one.
Why do you use an active buffer stage? I remember seeing your measurement chain you had posted a few posts back, with photos. I think there was an active buffer in that chain.
The buffer was (would be) the ideal location for the LME49990. That change in my Shibasoku's made a big difference on the active notch filters. if the impedance is low then you get a benefit. The lower noise and distortion can shine. Unfortunately the LME49990 did not survive and the $$$$$$ for a new mask set cannot be justified.
The OPA1611 is similar but not quite as good it seems. The LME49990 had a GBW of 110 MHz which does make a difference at higher frequencies. However its large input transistors are not compatible with Victors oscillator. Both noise and a tendency to oscillate in higher Z circuits.
Well, the point for passive/active notch is the need of the input buffer to drive the T-Notch R/C circuit. Bootstrapped T-Notch will be the best active circuit (against TI paper) to choose the Q as the 2. Harmonic will not reduced as Q about 8..10.
This means, to lower the resistor noise a good input T-Notch driver is required f (THD & Noise & Level). I do not like to drive the LDO, as using balanced LDO connection, to have any influences/impact do the T-Notch load (none buffered). Active or none active behave here equal.
Also the used cap brand as resistor brand will be important. Any resistor pot's to tune up, will degrade the notch over time. Also I do not like to use any dual opamps, do the channel cross talk.
Hp
The active linear buffer is located after the passive notch filter for to amplify the distortion signal.
I'm guessing this might work better if a Schottky diode is used, due to its lower forward voltage.
Cheers,
Bob
Yes. Ed Simon mentioned some vintage 'RF hot carrier diodes' which are just Schottkys of course.
Jan
Jan
The trouble, or maybe not, is schottkey diode have much larger junction capacitance which may interfere.
Current version of Hot Carrier Diodes!
https://www.onsemi.com/pub/Collateral/MMDL301T1-D.PDF
Use a biased pair and look at the difference between the one with added RF and the dry one. You can detect well below a millivolt of RF.
They might even be popular, Digikey has more than 100,000 in stock! But it will run a bit more than $10.00 for a hundred.
https://www.onsemi.com/pub/Collateral/MMDL301T1-D.PDF
Use a biased pair and look at the difference between the one with added RF and the dry one. You can detect well below a millivolt of RF.
They might even be popular, Digikey has more than 100,000 in stock! But it will run a bit more than $10.00 for a hundred.
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Please look in the OPA627 data sheet:
Applications-
Precision Instrumentation
Fast Data Acquisition
DAC Output Amplifier
Optoelectronics
Sonar, Ultrasound
High-Impedance Sensor Amps
High-Performance Audio Circuitry
Active Filters
Very nice Simon, thanks. Now if only the USD would tank I can get back into electronics.
Got a lot of time on my hands for the few months.
Got a lot of time on my hands for the few months.
Maybe this could be turned into a Group project, an Oscillations Sniffer.
Ed, how does the actual circuit look then, can't visualize it well.
Jan