Set a push-pull output to high impedance

Hi everyone,

I'm trying to design a simple emitter/receiver on a same wire, and my output stage of the emitter is a push-pull like that :

The problem is, when I'm receiving data, I don't want 90% of the signal go to the push-pull output, because this one have a really small output impedance (something like 60 ohm).
Is it possible to add 3 or 4 components to set the push-pull output to high impedance? I tried to stop the current bias, but it juste made the output impedance rise to 200-300 ohm...

Thank you!

On a TTL Tri-state output, they usually turn off the output transistors, you can achieve the same thing by base of Q12 to V+ and the Base of Q11 to ground. Millman shows a logic gate with some diodes to isolate the tristate drive when you don't want it.

I’m wondering if some schematics of tri-state IC’s would help. like 74HC244

gate.jpg

Ok I understand, does this work when I have an analog signal on the input too?

Take a look at this for ideas on isolating the Q11/Q12 junction from the RL2 load.
http://www.analog.com/static/imported-files/tutorials/MT-088.pdf

"Ok I understand, does this work when I have an analog signal on the input too?"
As long as the analog signal is small enough to not override the high impedance bias.

Ok great, thank you very much!