Ahh, I get it now. Then why not just a fast comparator?
http://cds.linear.com/docs/en/datasheet/1016fc.pdf
http://cds.linear.com/docs/en/datasheet/1016fc.pdf
Hahaha, the lm381 was the first in the kicad library, here it is with the correct part number for the opampsMagnet has declared a moratorium on part numbers.
The spec sheet says 5V to 12V (12.6V absolute maximum) for the power supply.I'm unsure if the part you linked has the necessary voltage inputs
I was referring to the comparator from ronv, the output voltage is only guaranteed to go up to 2.7The spec sheet says 5V to 12V (12.6V absolute maximum) for the power supply.
Single ended or split, as you wish.
ps, that comparator from ronv looks good, too.
odd, for some reason those didn't show up in my search results... mouser definitely carries them though, thanks for pointing it out!You can choose 74HC4020, 74HC4040.
That makes sense, thank youNo. Your offset control will change the gain. You need the offset on the +in so it is not in the gain determining current path. That forces the configuration to be inverting.
also makes sense, thanksConnect your amplitude control to -in like a volume control and your offset on the +in
This immediately causes a problem with DC offset being applied to the -in by the amplifier chip so you need another coupling capacitor to avoid DC feeding back into your divider.
I realized after I posted the schematic that I neglected to put a resistor in line with the potYou can not allow the amplitude control to go to zero ohms like that rheostat you drew because the gain would be infinity in an inverting configuration. Use the amplitude control as a voltage divider and then put a relatively high ohm resistor to the -in pin. Choose the amplitude pot to be as low a resistance as the divider will drive then use a higher resistance to the -in pin. That method will keep the inverting configuration from loading down the voltage on the wiper. Maybe 2k for the pot and 50k for the input resistor.
Thanks!Something like this:
I'm not sure what you're getting at with the first part, I've never messed with high frequency amplifiers before thisWow, Like most really high frequency amplifiers they would rather oscillate than amplify. I would worry about that and the response time when you use it as a comparator and it saturates against the rails. I didn't see that in the spec sheet. Are you building it on a PCB??
That should work. It's just not the way I would do it. Your gain range is .4 to 2.76 You could get a lot more range with the circuit I posted, 0 to dozens.are there any downsides to the attached circuit?
other than it can't take the amplitude all the way to zero?
(just trying to learn with this one)
thanks for the links!Hello,
When you are still prototyping, you could use tha manhattan art prototyping.
In this post in the tips and tricks thread I posted some info on it:
http://forum.allaboutcircuits.com/showpost.php?p=152539&postcount=29
Bertus
gocha, and agreed, just wanted to make sure I understoodThat should work. It's just not the way I would do it. Your gain range is .4 to 2.76 You could get a lot more range with the circuit I posted, 0 to dozens.
When I want to do a stage that can't go to zero gain, I use a non-inverting configuration and put the pot in the feedback loop. Gain = 1+ Rf/Rc and I can dial Rf down to zero to get a gain of 1.
I didn't have a 50 ohm on hand (all at school)You may need a 2 layer board with a ground plane.
What happens is the output signal rise time is very fast so any capacitance looks like a small resistor. Since the bandwidth is so high the chip can amplify this and go into oscillation. To combat this you need a really tight layout with nothing from the output getting close to an input or the feedback pin. Also if you use large resistor values like you have the ratio of the capacitive reactance to the input is bad, so you need to use low value resistors to set the gain and your source needs to be a low impedance. Where your signal generator pictures driving a 50 ohm resistor? If not go see what it looks like driving 50 ohms.
Take a look at the datasheet examples in figure 65 & 66 for some examples.
Make sure that the gain is not so high that the output swings to it's maximums or it will take it a long time (50ns.) to switch back to the other polarity. You could, I guess, follow it then with a fast Schmitt trigger.
http://cds.linear.com/docs/en/datasheet/1016fc.pdf
Now you're talking about something I know about!Geeze, don't do that! You can smoke the output amplifier of the signal generator by attaching just any old resistor you have laying around. I know because I've done it.
If the output impedance is 50 ohms, lower the resistance of the parts in my drawing to accommodate that. 50 ohm pot, around 1k for the gain resistors. At 10 MHz, you're fighting capacitance problems and the lower resistance reduces the frequency of the poles created by parasitic capacitance.
ps, don't use a 50 ohm pot for the offset. That would require a 5 watt pot. Better a bit of mismatch on the inputs than a burnt potentiometer.