The OPA544 and OPA541 have some desirable features but I think I will go for the OPA564, it has only a +-12V supply capability(the original design uses a OPA544 and +-35V) but it has far higher bandwidth(full power bandwidth of 1,3MHz at gain = +2, OPA541 have a full power bandwidth in the lower kHz range) but the OPA564 features only 1,5A(1,5A @ 20Vpp output with +-12V supplies) so maybe I'd like to parallel two of those.
As far as offset is concerned the OPA564 has the following:
OFFSET VOLTAGE(V
CM = 0V):
Input Offset Voltage(V
OS): typ ±2mV, max ±20mV
vs Temperature(dV
OS/dT): ±10µV/°C
vs Power Supply(PSRR): typ 10µV/V, max 150µV/V
INPUT BIAS CURRENT(V
CM = 0V):
Input Bias Current(I
B): typ 10pA, max 100pA
vs Temperature see figure in datasheet...
Input Offset Current(I
OS): typ 10pA, max 100pA
Common-Mode Voltage Range(Linear Operation): (V-) to (V+)-3V
CMRR min 70dB, typ 80dB
Slew Rate(G = 1, 10V step): 40V/µs
THD+N(f = 1kHz, R
LOAD = 5Ω , G = +1, V
OUT = 5V
P): 0,003%
I very much like the idea Klaus wrote about, I have been thinking about how to come up with a triangle/ramp waveform with mV's of peak-to-peak amplitude but thus far all I have thinking about is RC generated waveforms and the basics of how analog PWM modulation works which I am not sure will be of much use.
But so that I am sure I understand, the other idea others have been talking about, could that be called a "composite amplifier"?
Which I have seen examples of where they used a amplifier with high DC accuracy to enhance a high-bandwidth amplifier, I don't understand how to combine two other op-amps like that but this might be a good opportunity to learn more about that?
If the 2nd idea is a composite amplifier then I am leaning towards that, but in any case I have great use for the idea from Klaus in a couple of other projects, that idea will be quite fun to implement I think.
If I took the route of using another op-amp to compensate the offset, then there could be other benefits also I presume?
- - - Updated - - -
This is the original schematic, published by:
Nandkishor Ghodke
*, S. N. Kane
#, S. S. Khinchi
# and Ajay Gupta
*
*UGC-DAE Consortium for Scientific Research (formerly known as IUC-DAEF)
University Campus, Khandwa Road, INDORE – 452 001 (MP), INDIA
#School of Physics, Devi Ahilya University, Khandwa Road Campus, Indore
(the first time I loaded this image in the actual post it took something like 25 seconds to load)
I haven't drawn my own schematic yet because I am still deciding about the op-amp and I haven't yet decided upon how to implement the dual 3PDT switches(I think that's right) and the two dual DPST switches.
I will probably go with ordinary mechanical switches for the 3PDT's and relays for the DPST's, but I am considering alternatives to make the thing entirely digital in it's user interface, but I wouldn't mind a couple of nice mechanical switches but I would then also want indicating LED's for which state there in which demands switches with 3 individual switches in each so the third can switch LED's.
If I am not mistaken the buffer op-amp would need to be able to supply at most 200mA which would make it very expensive to use another power op-amp for that buffer unless I would have a dual power op-amp and only needed one of them for the output amplifier.