Hello everyone.
I'm working on a VCO project inside a LTSpice and I have a little problem with the quality of my wave.
It is the classical VCO solution with a NE555 configured as schmitt trigger comparator. I don't use a BJT but CD4066 because I want a low offset voltage.
Please help me to understand the reason why.
Range of frequency: 0.2V-20V of Vin for 200Hz - 20kHz.
+Vcc = 15V so I have a triangle wave from 5 to 10V, between the timer's thresholds.
As opamp I have OPA277, powered to +15V and -15V.
The reason why I put C2 is because I want to filter spikes present especially at 20kHz (20V of Vin) - see the image.
Where do these spikes come from? I also noticed that if I increase R1 and R2 (10x times) (and therefore decrease C1 to have same time constant) I don't get any spike but it also tends to be slower and have the peaks of the triangle a kinda curved. This is why I want to keep low resistors.
But I don't know where spikes come from and is it proper to filter them like that?
I'm working on a VCO project inside a LTSpice and I have a little problem with the quality of my wave.
It is the classical VCO solution with a NE555 configured as schmitt trigger comparator. I don't use a BJT but CD4066 because I want a low offset voltage.
Please help me to understand the reason why.
Range of frequency: 0.2V-20V of Vin for 200Hz - 20kHz.
+Vcc = 15V so I have a triangle wave from 5 to 10V, between the timer's thresholds.
As opamp I have OPA277, powered to +15V and -15V.
The reason why I put C2 is because I want to filter spikes present especially at 20kHz (20V of Vin) - see the image.
Where do these spikes come from? I also noticed that if I increase R1 and R2 (10x times) (and therefore decrease C1 to have same time constant) I don't get any spike but it also tends to be slower and have the peaks of the triangle a kinda curved. This is why I want to keep low resistors.
But I don't know where spikes come from and is it proper to filter them like that?
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