# recognising patterns in TTL logic analog circuit

There is a circuit based on TTL( transistor transistor logic I think) . The signals at points A B C D are described. I am new with this TTL, could you help me decompose this united circuit into the logic components which it consists from? Thanks.

• Looks more like RTL (Resistor-Transistor Logic). Cute, the PNPs are "upside down", but so is the supply; reminiscent of 50s-60s era germanium circuits. Commented Mar 30 at 8:25
• Hello Mr. Williams, what is the structures you see in here which is combining this circuit?Thanks. Commented Mar 30 at 9:42
• Could you explain what V_CON is, and what J11-J14 are or what might be attached to them? Commented Mar 30 at 10:38
• Hello Mr Williams, I think the X means that Vcon is non relevant.Its attached J11 is i think going to be attach to a gate of a mosfet. Commented Mar 30 at 11:41
• Hello Mr Williams, what is the substructure logic here? Commented Mar 30 at 14:27

It seems to be a simple inverter.

Assuming no other connections, resistors and supply as shown, we can simplify the circuit as so:

simulate this circuit – Schematic created using CircuitLab

which has a DC transfer function from V1 (A) to D,

give or take the setting of your R13, here set all the way towards C.

It's more or less an emitter follower-buffered negative-voltage (PNP type) RTL inverter, with level shift at the input.

The Darlington follower (Q2 into Q3) doesn't seem very useful, but without knowledge of application and ratings, that's neither here nor there.

• Hello Mr. Williams, point A is a pulse of 0-3.3V at 120ns.I am trying to understand and simulate each step. given my original circuit could you please explain what is the logic from point A to B? they have an intresting diode in parralel with capacitor, and some things near the -2.5V power supply. whatis the logic in that?Thanks. Commented Mar 30 at 19:12
• There is no logic function, simply a level shift. You can simulate the circuit to see voltages. LM4040 is a 2.5V regulator that has been replaced here with a voltage source. Commented Mar 31 at 1:15
• Hello Tim, so between A and B is a level shifter. what is the analog logic of the part show between the two arrows in the attached link? ibb.co/Rv19L07 Commented Apr 2 at 17:33
• That's the Darlington emitter follower part. Commented Apr 2 at 18:14
• Hello Tim, I want to simulate the level shifter part from points A to B however i dont know what input pulse its intended for and what output value it supposed to produce on point B. Could you please say what input signal to use and what output value on point B should i expect on the otput? Thanks. Commented Apr 3 at 9:25