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I've made simple circuit - it attenuates the signal 10 times, bare bones voltage divider:

schematic

simulate this circuit – Schematic created using CircuitLab

Now I want to bias the signal to half of my system voltage. I tried using another voltage divider(with equal resistors) for that or TLE2426 chip, which is used specifically for dividing voltage in half. I applied bias voltage(i.e. virtual ground) as in circuit below.

schematic

simulate this circuit

When I used the TLE2426 chip I used this circuit:
enter image description here

The question
For example I have 3.3 voltage system, so I have 1.65 virtual ground in the middle applied to Vbias. I have the following measurements on the Output:

  • When Input is floating - Output is 1.48 V
  • When Input is connected to system GND - Output is 1.36 V

This is pretty much the same with either TLE2426 or simple voltage divider biasing. I understand that in theory when I ground the input I divide this 1.65 volts with my 900k/100k divider, hence I should get 1.48 (I probably get 1.36 because of non-ideal resistors). For floating input my own explanation that float is close to GND, but not exactly, hence the difference...

Anyway the real question for me is - how can I get 1.65 volts on the output when the signal is grounded(or floating, but not necessary). Obvious solution for me is to take trimmer resistor and use it as a divider to get 1.65 point, but this seems like a cheap workaround, I would like to know if there is a away to make it with TLE2426 chip, after all it is made for this kind of things.

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You're under the TLE2426's voltage limits, declared on the front page of its data sheet as 4 to 40 V. You therefore should not expect it to do what you want at 3.3 V.

If you want the virtual ground to operate to lower voltages, you'll have to choose one of the other circuits on the page you got the TLE2426 schematic from. The Sijosae BJT-based virtual ground buffer should do better at such low supply voltages. It wasn't designed for such, but if it doesn't work as originally designed, it's flexible enough to be adjusted to work, since it's made of discrete components.

All of that aside, further discussion shows that the problem is that you want to connect the Input of the voltage divider to a signal that may hover around the same ground you're connecting the TLE2426 COM point to. That will try to drag the TLE2426 OUT below ½ TLE2426 IN, the amount depending on the output drive strength of the TLE2426 and the resistor values you use.

The solution is to prop the TLE2426 up somehow, such as by a diode:

Propped-up TLE2426

Then you use the biased-up virtual ground point (roughly 2.8 V above PSU ground) as your virtual audio ground. If you need to get closer to 2.6V, then you'd need something a bit more clever than a diode to bias up the TLE2426 COM point.

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  • \$\begingroup\$ oops, I missed 4 to 40 V somehow... it gives 1.65 V so I thought it is ok... thanks! But nevertheless, I tried it with 5V and it still gives "wrong"(undesired) output, it gives 2.25 V now. So if applied like this any voltage acts upon 900k/100k divider, doesn't matter if it is TLE2426, voltage divider or Sijosae buffer. I guess it is inherently wrong way to do so. As of what the other circuit does - there is no other circuitry yet, I'm just trying to figure out how to make this basic block work properly, at least for DC. \$\endgroup\$ – ScienceSamovar Mar 20 '17 at 0:59
  • \$\begingroup\$ So what about my questions in the final paragraph? It matters; for instance, if you're trying to pull more than about 25 mA, you're violating a different spec in the data sheet. That's why some of the other circuits on my virtual ground page (hi, author here) use the TLE2426 behind a stronger buffer. \$\endgroup\$ – Warren Young Mar 20 '17 at 1:01
  • \$\begingroup\$ Since I am measuring with multimeter for now I barely draw any current due to high multimeter impedance. Same would be for op-amps or any other high impedance load. Anyway - no circuit is connected for now at all. Moreover the reason the ouput is "off" is obvious - the voltage drops on the divider, so the whole circuit needs to be different I guess. And again - it is the same without TLE2426(i.e. with voltage divider splitting the rail). \$\endgroup\$ – ScienceSamovar Mar 20 '17 at 1:04
  • \$\begingroup\$ Draw your whole circuit; don't make us guess. Show the voltages you're measuring at each point with annotations on that circuit diagram. \$\endgroup\$ – Warren Young Mar 20 '17 at 1:09
  • \$\begingroup\$ um... You have the whole circuit in original post :D Its just your circuit for TLE2426 and "VGND" connected to "Vbias". Or you could change the TLE2426 circuit with simple resistor voltage divider(e.g. 33k-33k), which gives half voltage. For 5V it is 2.5 virtual ground, but Output is ~2.25 when Input is grounded. \$\endgroup\$ – ScienceSamovar Mar 20 '17 at 1:13

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