Hi everyone!
Im currently working on an analogue assignment where you take a square wave and convert it into a sine wave. So the method that is suggested and looks nice is to use a sallen-key low pass amplifier.
Now I have it done....if the world was ideal. My circuit works fine if I use resistors but because the second half of the assignemnt is to intergrate this thing into VLSI a 10Mega ohm resistor is not a good idea, unless you use a switched capacitor.
So I have designed and done the math!
R = 1/fC
R = 10 Meg
C = 10fF
Therefore f should be 10Mhz. Thats fine, I made a ring oscillator to do this. So I wire it all up (in S-Edit) and it just goes
It looks like that it has a considerbly lower resistance that it should. I checked the ring oscillator output, its fine. I replaced it with a function generator, nope, still same problem. If I remove the switch capacitors with resistors it works no question. What the darn is going on?
The program uses T-Spice to run (its the same as regular SPICE except it has thyme in it as well).
Here is the filter
Here is the switched capacitor
Im currently working on an analogue assignment where you take a square wave and convert it into a sine wave. So the method that is suggested and looks nice is to use a sallen-key low pass amplifier.
Now I have it done....if the world was ideal. My circuit works fine if I use resistors but because the second half of the assignemnt is to intergrate this thing into VLSI a 10Mega ohm resistor is not a good idea, unless you use a switched capacitor.
So I have designed and done the math!
R = 1/fC
R = 10 Meg
C = 10fF
Therefore f should be 10Mhz. Thats fine, I made a ring oscillator to do this. So I wire it all up (in S-Edit) and it just goes
It looks like that it has a considerbly lower resistance that it should. I checked the ring oscillator output, its fine. I replaced it with a function generator, nope, still same problem. If I remove the switch capacitors with resistors it works no question. What the darn is going on?
The program uses T-Spice to run (its the same as regular SPICE except it has thyme in it as well).
Here is the filter
Here is the switched capacitor