Op Amp Grounding question

[dxm1]

This is a fairly simple question, but I'm afraid the description may be long winded...

I'm using two OAs from an LM324 as a VFO. The circuit has two separate ground paths, decoupled with an RC network. The VFO is grounded to the "dirty" path. My 1/2 V+ supply is grounded to the "clean" path.

Normally I would terminate unused OAs as voltage followers, with the + inputs tied to 1/2 V+. In this case, that would put the return though the "clean" ground path.

Soooo, my question is this: would it be wise to construct another voltage divider (across the "dirty" ground path) just to terminate the unused OAs? That would be my first instinct, but I would like to hear the pros and cons of both solutions. Granted, two resistors and a cap are pretty cheap insurance, but limited board space has forced me to consider a compromise...

[brett]

I don't have an answer, but have two questions:
Why not use an LM358 or another chip without excess op-amps?
Why would unconnected OAs cause a problem?  I suspect people duals as singles and leave the extra OA "hanging".
cheers

[dxm1]

I don't have an answer, but have two questions:
Why not use an LM358 or another chip without excess op-amps?

I tried a TL072, and it didn't work well in this circuit. It may be fine if I were using a bipolar supply, or it may be BJT vs. FET inputs. I don't know. I do know that the LM324 works. An LM358 would probably be just as good, but I don't have one. I _do_ have about 150 LM324s...

Why would unconnected OAs cause a problem?  I suspect people duals as singles and leave the extra OA "hanging".
cheers

Maybe I'm just being anal, maybe it's a product of old CMOS design habits. I've heard rumors that not terminating unused OAs in a multiple device package can lead to induced noise in the operational OAs, as well as the potential for increased current consumption. If it wasn't for the fact that when I placed the components for the PCB layout the LM324 was squeezed down into a corner of the board, I would just add the divider (as I drew up the schematic). Unfortunately, adding these three components and their traces will require me to  significantly rip and reroute...

Ah well, I guess I was just looking for an experienced opinion that mixing the grounds would be OK for the unused OAs, even though I know that "crossing the beams" of clean and dirty grounds is a no-no in mixed signal circuits. 

[brett]

not terminating unused OAs in a multiple device package can lead to induced noise in the operational OAs, as well as the potential for increased current consumption.

Cross-talk between the OAs should be very low. 
As far as I know, if you leave the output unconnected, the power consumption will be low.

Alternatively, what about +ve to Vbias and -ve to out ?