uA709 op amp compensation

[Joseph M. Zias]

Most likely this can only be answered by an "old timer". I am making measurements on an uA709 op amp (metal can). I would like to calculate the frequency rolloff curves (I can measure them). I assume the compensation is via the miller effect. To do the calculations I would need to know the gain of the transistors and the effective resistance seen at the compensation terminals, not including the values I put there.
Anyone know those values?

 

[berkeman]

So you have the opamp schematic entered into SPICE and are looking for the transistor model data?

 

[Baluncore]

Anyone know those values?

Do you have the full circuit for the uA709, or just the simplified diagram ?
Resistor values are here: https://lh.pe/file/UA709CN(1).pdf

 

[Joseph M. Zias]

I have the schematic but not a spice program. Will have to look into getting one. However, using the open loop curves of Fairchild and doing some backtracking I find:
With C1=10pf and R1=0, the breakpoint looks to be 10khz. That would give an equivalent resistance working with C1 of 15.9 k ohms.
With C1=100pf and R1=1.5k, the breakpoint looks to be 1khz. That also equates to an equivalent resistance of 15.9 K ohms; makes sense as the frequency changes by x10 as does the capacitance.
The crossover frequency of the R1C1 is about 1 Mhz, so that does not come into play until the 2nd breakpoints.
So, assuming gains of 100 for the internal stage I get an R value of 15.9 k ohms. I don't see how to arrive at that given the schematic, but I don't know how to analyze it in that detail. I am of course just guessing on the gains.

 

[Baluncore]

Here is an LTspice model for the uA/LM709. At the end it defines the transistors used as all having the same specifications.

* LM709 SPICE Model
* Datasheet: http://www.national.com/ds.cgi/LM/LM709.pdf
* Helmut Sennewald
*
* Input compensation B (8) ---------------------\
* Input compensation A (1) ------------------\  |
* Output compensation (5) --------------\    |  |
* Output (6) -----------------------\   |    |  |
* Negative supply (4) ----------\   |   |    |  |
* Positive supply (7) --------\  |  |   |    |  |
* Inverting input (2) ----\   |  |  |   |    |  |
* non-inverting input(3)  |   |  |  |   |    |  |
*                     |   |   |  |  |   |    |  |
.subckt LM709         In+ In- V+ V- OUT COMP A  B
*
Q7 v+ N001 N005 0 NPN1
R5 v+ N001 10k
Q3 N001 N006 N003 0 NPN1
Q4 N001 N003 N002 0 NPN1
R1 N005 N006 25k
R3 N003 N004 3k
Q15 N004 N004 N002 0 NPN1
R2 N005 A 25k
Q2 A in- N007 0 NPN1
Q1 N006 in+ N007 0 NPN1
Q5 B A N009 0 NPN1
R4 N009 N004 3k
Q6 B N009 N002 0 NPN1
R6 v+ B 10k
R8 N002 N011 3.6k
R10 N011 N010 10k
Q10 N010 N010 V- 0 NPN1
Q11 N007 N010 N008 0 NPN1
R11 N008 V- 2.4k
R9 N012 N011 10k
Q8 v+ B N013 0 NPN1
R7 N013 N012 1k
Q9 comp N002 N012 0 PNP1
R13 N014 V- 75
R12 comp N014 10k
Q12 N015 comp N014 0 NPN1
Q13 V- N015 out 0 PNP1
Q14 v+ N015 out 0 NPN1
R14 v+ N015 20k
R15 N012 out 30k
.MODEL NPN1 NPN (BF=100 VAF=50 RB=100 CJE=4P CJC=2P CJS=2P TF=0.5N TR=10N)
.MODEL PNP1 PNP (BF=15 VAF=50 CJC=4P CJE=8P RB=100 TF=20N TR=200N)
.ends LM709

 

[Joseph M. Zias]

Here is an LTspice model for the uA/LM709. At the end it defines the transistors used as all having the same specifications.

* LM709 SPICE Model
* Datasheet: http://www.national.com/ds.cgi/LM/LM709.pdf
* Helmut Sennewald
*
* Input compensation B (8) ---------------------\
* Input compensation A (1) ------------------\  |
* Output compensation (5) --------------\    |  |
* Output (6) -----------------------\   |    |  |
* Negative supply (4) ----------\   |   |    |  |
* Positive supply (7) --------\  |  |   |    |  |
* Inverting input (2) ----\   |  |  |   |    |  |
* non-inverting input(3)  |   |  |  |   |    |  |
*                     |   |   |  |  |   |    |  |
.subckt LM709         In+ In- V+ V- OUT COMP A  B
*
Q7 v+ N001 N005 0 NPN1
R5 v+ N001 10k
Q3 N001 N006 N003 0 NPN1
Q4 N001 N003 N002 0 NPN1
R1 N005 N006 25k
R3 N003 N004 3k
Q15 N004 N004 N002 0 NPN1
R2 N005 A 25k
Q2 A in- N007 0 NPN1
Q1 N006 in+ N007 0 NPN1
Q5 B A N009 0 NPN1
R4 N009 N004 3k
Q6 B N009 N002 0 NPN1
R6 v+ B 10k
R8 N002 N011 3.6k
R10 N011 N010 10k
Q10 N010 N010 V- 0 NPN1
Q11 N007 N010 N008 0 NPN1
R11 N008 V- 2.4k
R9 N012 N011 10k
Q8 v+ B N013 0 NPN1
R7 N013 N012 1k
Q9 comp N002 N012 0 PNP1
R13 N014 V- 75
R12 comp N014 10k
Q12 N015 comp N014 0 NPN1
Q13 V- N015 out 0 PNP1
Q14 v+ N015 out 0 NPN1
R14 v+ N015 20k
R15 N012 out 30k
.MODEL NPN1 NPN (BF=100 VAF=50 RB=100 CJE=4P CJC=2P CJS=2P TF=0.5N TR=10N)
.MODEL PNP1 PNP (BF=15 VAF=50 CJC=4P CJE=8P RB=100 TF=20N TR=200N)
.ends LM709

Looks like I am going to have to get LT Spice downloaded.

 

[Baluncore]

Any SPICE will do with that code, but LTspice, now from ADI, is probably the best at the moment, and is free.
Also, subscribe to https://groups.io/g/LTspice which is great for help with running LTspice.