TL084...

[Dr.EM]

Just a couple of questions out of curiousity. Is there any difference between the 074 and 084? Why is it on these models the power supply for negative is on the top? This seems to go against convention and looking at it, all they would have to do to make it with posistive on top is change which end the dimple in the case is. So I assume there is some deeper wisedom to it being that way round :?:

 

[Papabravo]

I'm confused. The VCC+ and VCC- are in the middle of the chip on a TL084. Which V- are you talking about? Oh...OK I'm rotated 90 degrees. There is no real convention on where power and ground pins go. Different IC designers from different companies can place the pads anywhere on the dice they feel like. Your job as a circuit designer is to never assume you know where power and ground are supposed to go. ALWAYS ALWAYS ALWAYS consult the datasheet.

The most obvious difference in looking at the data sheet is the Maximum Input Offset Voltage(V_sub_IO_max). You do know what that refers to right?

 

[Hero999]

TL074 is supposed to be lower noise but the specification on the datasheet is the same.

 

[Dr.EM]

I always assumed offset voltages refered to the op-amps internal deviation from the theoretical voltage. IE if I tied both inputs to 0v, the output will likely read 14mv or something. Your saying the 084 has a value closer to 0 or whatever it should be than the 074? This is only stuff I am assuming, we've never been taught op-amp characteristics nor have I researched them myself.

Those power supply connections still seem wierd though, seeing as how on the others in the series (081, 082 etc) have them with posistive on top.

 

[Nigel Goodwin]

Those power supply connections still seem wierd though, seeing as how on the others in the series (081, 082 etc) have them with posistive on top.

I'm confused as to what you mean?, I've just downloaded the datasheets for both devices and +ve is pin 4, and -ve pin 11, on BOTH the 074 and 084 series.

 

[Papabravo]

Dr. EM
I think that the input offset voltage is the voltage you need on the input to make the output zero. The smaller this maximum value, the closer to ideal the opamp is.

Top and bottom, left and right are relative terms. Unless we know where pin 1 is on your personal compass rose we have no idea what you're talking about. It's a senseless point anyway. Power and ground are where they are for the convenience of the chip makers and not your personal sense of right and wrong, wierd or comforting. Just get past it will'ya?

 

[eng1]

Yes, the input offset voltage is the dc voltage you must impress between the inputs of the op amp to have 0 V at the output. It is equal to the difference between the Vbe of the input transistors (in bipolar input op amp). It depends on temperature, difference between collector currents and difference between saturation currents.

 

[eng1]

The pin layout is the same for TL074 and TL084.
The are datasheets from different companies... where did you download yours from? TI decribed the TL074 as the low-noise version of the TL084, but I didn't find further explanations, since the spectral density of the equivalent input noise voltage is the same for the two devices.
When I evaluate noise I like to know both voltage and current noise spectral densities of the op amp.
However the total noise in an operational circuit is often dominated by thermal noise (resistors). If you want to minimize noise, assuming that there is a voltage source, you have to 1) keep resistance values low and minimize the number of resistors (if dc accuracy is not required, don't use balancing resistors); 2) minimize source resistance; 3) choose a bipolar input op amp for low source resistance (up to 10 kohm); 4) minimize the input capacitance (it increases the noise gain with resonant peaking).
With current sources it is different.

 

[Hero999]

I have datasheets for both the TL084 and TL074 and they are both from Texas Instruments.

 

[Nigel Goodwin]

I have datasheets for both the TL084 and TL074 and they are both from Texas Instruments.

They are only one of a number of manufacturers, if you google for datasheets you can download various ones - but all are (obviously) compatible.