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Quad single supply opamps that can handle negative input voltages

HighTechPower

Member level 5
Hi guys. I have to make a circuit utilizing a quad single supply opamp which can handle negative input voltages at least up to -12V. Any idea which easily available quad opamp supports this function. The supply voltage is +15V (pin4), 0V (pin11).

Hi,

I don´t know any.

But I´ve always found a solution to such a problem. Problem with specification.

Klaus

Hi KlausST. I have not drawn any diagram yet. However I know that voltage at noninverting and inverting input will be -10V and -12V respectively

Simple method to accommodate (Level shift) a - V into a single supply OpAmp input :

Look at TI Excel sheet first....

Regards, Dana.

Attachments

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• TI Voltage Divider.zip
302.3 KB · Views: 41
for telecom. The way past the negative input (for me)
was to use the buffered vref as "ground" and a return
for feedback signal, use Vss as the "reference" for
error amp (feedback through a resistor divider to Vref).

Clamp that feedback node to well less than a diode
Vf (I used a MOS follower, drain from Vdd, cheesy
gate divider to get "just enough" below ground to not
affect Vio by leakage but keep substrate injection from
happening).

However I know that voltage at noninverting and inverting input will be -10V and -12V respectively
This is not a linear mode to have any difference on the inputs unless this is job for a comparator which is trivial to choose.

Since you have not stated any other design specs, I can solve the obvious problem with either a clamp to 0V or operate in linear mode with Av =- 1 then both inputs will be 0V.

make a circuit utilizing a quad single supply opamp which can handle negative input voltages at least up to -12V.
Can the input voltage also go positive?
What is the full input voltage range?
What output do you want from the two inputs?

No op amp will work with voltage at their inputs below the negative supply rail (0V here), but there are ways to handle negative signal voltages.
If you answer the questions in my previous post, I can better answer yours.

Define all input and output functions with transient conditions that need to be attenuated for protecting the IC outside it's operating range.

That means AC, DC signals source impedance and transfer functions.

If you need accurate linear functions then a negative Charge Pump and LDO may be necessary but it you cannot define the task, then design solutions are impossible. The first rule of professional design is to define the form, fit and function with all necessary context assumptions of the task in Design Specs.

Thank you guys, I have learned how to implement negative input voltages by applying offsets for single supply quad opamp. However would like your suggestions that is there any better opamp than LM324 in terms of better results while applying offsets in SOIC-14 package? The single supply working voltages should be +12V or above.

You have no target specs as to signal accuracy, bandwidth, range, load, source
signal is being used for .....

Regards, Dana.

No op amp will work with voltage at their inputs below the negative supply rail (0V here), but there are ways to handle negative signal voltages.
If you answer the questions in my previous post, I can better answer yours.
Hi Crutschow, Is not it true that MC34074 can operate with negative input voltages while in single supply mode without using offsets? Plz see attached datasheet. This is what it says on first page,
"Although this series can be operated from split supplies, it is particularly suited for single supply operation, since the common mode input voltage range includes ground potential (VEE)".
--- Updated ---

Almost same wording for LM324 see attachment first page. However in table it says common mode range -0.3 to 32,
"The common mode input range includes the negative supply, thereby eliminating the
necessity for external biasing components in many applications."
--- Updated ---

Can the input voltage also go positive?
What is the full input voltage range?
What output do you want from the two inputs?
No both input will remain negative
-10V to -12V
Positive output around 5V

Attachments

• MC34074.PDF
455.1 KB · Views: 41
• LM324-D.PDF
306.6 KB · Views: 112
Last edited:

Thrashing around w/o adequate description/design goals will not allow forum to help :

1) Single supply opamp configuration, Inverting, Non Inverting, Differential, what is it ?
Post a schematic.

2) For 1) what gain do you want ?

3) For 1) What is the input range V you want ?

4) For 1) and 2) what is output V you want ?

5) For 1) what is BW of signal

6) For 1) what is load on opamp ?

7) What is source of input signal, and its electrical description ? Z, range, BW....

Thrashing around w/o adequate description/design goals will not allow forum to help :

1) Single supply opamp configuration, Inverting, Non Inverting, Differential, what is it ?
Post a schematic.

2) For 1) what gain do you want ?

3) For 1) What is the input range V you want ?

4) For 1) and 2) what is output V you want ?

5) For 1) what is BW of signal

6) For 1) what is load on opamp ?

7) What is source of input signal, and its electrical description ? Z, range, BW....
1) Differential, diagrams not drawn yet
2) 2.5 gain
3) Perhaps -7V to -9V
4) 5V output
5) BW not critical
7) DC current on negative rail

Supply voltage +12V to 0V single supply
--- Updated ---

I prefer not to add any offsets so want to confirm if MC34074 will work fine for this job?

Last edited:

So for a -9 to -7 input differentially you want 0 to +5 output, just to confirm ?

Regards, Dana.

So for a -9 to -7 input differentially you want 0 to +5 output, just to confirm ?

Regards, Dana.
Yes

Hi,
Is not it true that MC34074 can operate with negative input voltages while in single supply mode
I can´t find any information that the MC34074 can handle negative input voltages with respect to it´s VEE.

You need to differentiate between OPAMP_input or your circuit`s input voltage range.

The OPAMP usually can´t handle negative input voltages, but if you design your circuit correctly, the circuit can handle negative input voltages. But this is circuit depenent, thus you will not find this information in the OPAMP datasheet.

Klaus

This workable (note I used LM324 as I dont have your model. Note I assumed you have a +15V supply.
How accurate do you need the circuit to be, input to output ?

You can of course scale the input R's to scale the input Z if needed, within bounds of OpAmp bias
created offset issues.

Last edited:

Hi,

Output to be expected 0V ... is not a valid requirement, since no OPAMP can fulfill this (unless it has negative supply voltage). Even a Rail-to-Rail-Output-OPAMP just comes close to the rail.

***
When using "Offset" to pull up the input, then - if you want some decent accruacy and precision - don´t rely on the power supply. A power supply is neither accurate nor precise. It is expected to be noisy and will drift with time, temperature, load current ...

All this errors you will see at the OPAMP output. maybe even amplified.
--> better use a voltage_reference_IC.

is there any better opamp than LM324 in terms of better results
--> Give your requirements as numbers

Klaus

Response to last post in thread :

The power supply as a reference, if your A/D has a reference use that
to measure supply to get correction. You can even power many micros these days
with precision references and other analog.....

Or just use a Vref part to power the divider that is contributing error otherwise.
Or one of the OpAmps in the quad and use that to scale up for the divider.

Here is an opamp with bipolar output that gets ~ a few mV off rail, no load.

CMOS OpAmp gets even closer, again no load (some with 1 mV 100K load), but not
zero due to its Rdson of output driver and leakage.......

Of course rail to rail is an apparition, even with OpAmp powered with negative supply.
Noise prevents that from being true.

Regards, Dana.