show pins

[letitbleed]

Good afternoon. I put a lt1112 in design but I need to connect pins 6 and 8, which are not shown. How can I do it? It show all pins except those

[KIKEV89 · Accepted solution]

Hello letitbleed

You need to add another component, when you place a LT1112 will appear a menu like this (attached image), you have to select, new A and then new B

you will get some like this(second attached image)

Greetings

[letitbleed]

I'll try to do that and post if anything comes up. Thank you very much!

[letitbleed]

Hello. I wish to simulate a Phase shift oscillator but it doesn't seem to work because i get 0 voltage at the output all the time. Is is just not possible to simulate this? Thanks in advance. 

[jg_geadinc]

You will run into this frequently when simulating oscillators in Spice. Spice is an ideal environment and oscillators rely on the transient of the power supply coming up and noise to give them a 'kick' to get started. There are a few ways to do this in simulation, I usually use a delay on the power supply so it is applied after the simulation has started. Either use an interactive switch, or a time-delay switch. This will also allow you to see if it does not have enough gain or the right amount of phase shift to sustain osciallltion. 

[letitbleed]

This is the design. Where can I implement the time delay switch?
(I know the potentiometer should be a 29 k resistor but I usually set it in 10% so its is equivalent)

[jg_geadinc · Accepted solution]

Since you are using a virtual opamp it is easier just to give it a kick start like this. If you were using an opamp where you need to provide power, you can switch the power on like this. 

The switch is the TD switch (time delay) from the library. 

[letitbleed]

Oh my... THANKS! I had tried to kick start it with making the gain greater than 1 (potentiometer greater than 29) but all to no avail. You are absolutely my hero! Could you supply more info on why this is the way it is? (Some other thread or a webpage with more detail on this). Anyways, I am very grateful

[jg_geadinc · Accepted solution]

As I mentioned in a previous post, real life oscillators have noise to help them get started. Also the slope of the power supply coming up also helps provide a transient to get things started. Because of absolutely noiseless attributes of ideal components in Spice, the circuit is just sitting there, because it is stable at DC. Once a transient is introduced, the delay of the R's and C's mean this transient gets amplified and the feedback to the input to cancel it is delayed which allows it to build to a value larger than it was initially resulting in oscillation. 

You can play with the value of the 5V input to see just how small it can be to get things started. Make it small enough and you will be able to see the oscialltion grow. Try .001uV. 😉

[letitbleed]

Barkhausen's criterion for oscillation is neccessary but not enough... This awesome.  Why does the amplitude increase when I reduce the kick-starting noise?