CD4069 oscillator in LT Spice

Papabravo

Joined Feb 24, 2006
16,835
Oscillators rely on a variety of small effects to get started. These effects are often missing from simulations with ideal components. They are "too ideal" to oscillate. Techniques range from introducing parasitic elements to noise into the simulation.
 

Papabravo

Joined Feb 24, 2006
16,835
Didn't know what pin that 'extra' pin was, so I assumed it was the supply pin. How shoul;d I draw it?
It is for unconnected inputs. The voltage that the device uses defaults to 1 volt. It is set by a device parameter.
Read the Help page for the "A" devices. Here is an excerpt:

A. Special functions.
INV, BUF, AND, OR, and XOR are generic idealized behavioral gates. All gates are netlisted with eight terminals. These gates require no external power. Current is sourced or sunk from the complementary outputs, terminals 6 and 7, and returned through device common, terminal 8. Terminals 1 through 5 are inputs. Unused inputs and outputs are to be connected to terminal 8.


I would connect it to GND
 

Thread Starter

dotneck335

Joined Apr 5, 2021
19
I did connect it to ground. Got this message: "time step too small; initial timepoint: trouble with buf-instance a1". Still no oscillation
 

Papabravo

Joined Feb 24, 2006
16,835
In your opinion, how accurate are these models? A 4069 for example?
They are behavioral models. You can read read the actual text files that implement them. Besides the logic functions they model propagation delay, rise time, fall time and voltage levels. In some cases they use the LTspice OTA devices and in other cases they use a combination of ideal components with generic parameters. Here is the one for the 4069. It uses two diodes, a resistor, a capacitor, two MOS transistors, one n-channel and one p-channel, and a final capacitor. What do you think?

.subckt HEF4069UB a out VDD VSS params: speed=1
D1 A VDD di
D2 VSS A di
R a o 700
Ca o VSS {10p*M} Rpar=1G
M3 OUT o VSS VSS HEFn
M4 OUT o VDD VDD HEFp
C4 OUT VSS {10p*M} Rpar=1G
.model di d vfwd=0.5 ron={100/M}
.model Hefn vdmos vto=1.3 kp={speed*1.1m*M} lambda=15m rs={50/speed/m} mtriode=2.5
.model Hefp vdmos pchan vto=-1.5 kp={speed*1.1m*M} lambda=45m rs={70/speed/m} mtriode=1
.ENDS
 
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