# nand gate astable vibrator do not work at 400kHz

I want to build a 400kHz square wave oscillator with NAND GATE using the CD4011BE circuit.
Unfortunately, it does not work as expected when I use R2 and C values according this schematic:

Vcc = 5V
R1  = 1Mohms
R2  = 1100ohms
C   = 1nF

Expected: Fosc = 1 /(2.2*1100*1E-9) = 413,223kHz


The signal on the 2nd NAND Q output stay at 5V with small noise oscillation (seen on scope).
But when i replace R2 by a 10Kohm resistor, there is a real square wave signal around 45kHz.
So, what is the problem with the 1.1kohm ?

Thanks for help !

• Did you measure the actual resistance of the resistor? Typically, resistors have some error in its true resistance value. Basically, your 1.1kOhm resistor may not actually equal exactly 1.1k... It could be 1.05k or 1.15k or something... That goes for your capacitor as well. Check the actual values of your components. – KingDuken May 15 '18 at 0:36
• From looking at DC bias , why do you think it fails? – Sunnyskyguy EE75 May 15 '18 at 0:55
• Do you think the ESD input diodes interfere? – Sunnyskyguy EE75 May 15 '18 at 1:10
• I can adjust R2 with a 220ohms potentiometer added to 1000ohms resistor. I don't know what you are talking about ESD input diodes...?!!! – Teddol May 15 '18 at 2:04
• Please, help... – Teddol May 15 '18 at 14:44