Texas Instruments notation question

[BurnedResistor]

Dear All,

I am working on designing an amplifier to alllow for the scaling in the for of y = mx-b, and found a TI reference manual:s"
http://www.ti.com/lit/an/sloa030a/sloa030a.pdf

However, in the appropriate section, on pg12 the book uses a notation that I have never seen before in Analog design: R1 || R2

I am guessing that this is not a logical bitwise operation?

I was not able to find out what this notation meant :/ Anyone got any ideas?

[BurnedResistor]

Similarly they state

R1 || R2 << Rg

Again i really dont think the << is a bitwise shift. Anyone know?

[Phoenix]

|| means in parallel
<< significantly less than (orders of magnitude)
>> significantly greater than (orders of magnitude)

[BurnedResistor]

Oh wow thats pretty neat!

In other words, R1 || R2 << R3

R1 and R2 in parrallell are 2 orders of magnitude smaller than R3?

[dmills]

I don't think << necessarily means TWO orders of magnitude so much as the less precise "LHS Much smaller then", how much smaller depends on how close you need the approximation to be.

It could be 1, 2,or 3 orders, but is it uncritical as long as R3 is a lot bigger.

I would note that there may be other constraints, so don't get silly, output drive, input bias current, thermal noise.... But the simplification in the maths works as long as R3 is much bigger then R1 || R2.

73 Dan.