Comparator input below V-

Question

I am searching for a way to use a comparator with possible negative voltage on its inputs.

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My thoughts and attempts so far:

• Op amps and comparators with V+, V- and GND: the circuit utilizes a single LiPo battery.
• LM339/393: works correctly only when Vin>= V- - 0.3V, which is not enough.
• Diodes: too low voltage, I suppose

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Requirements are:

• Vin range -2.0V .. + 2.0V (and around 0.1V on the reference)
• Max. current provided for comparator input: around 500 uA

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Recently I have found an interesting comparator - LT1716 (datasheet/website). It provides a "Valid Output with Either Input 5V Below V– ". If there is one, then the idea is not new and there should be more, right?

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(I am new to electronics, and I am sorry if I did not provide some related info - please let me know what I forgot)

• Voltage Spike: Hi, welcome to EE.SE, there is one problem with your question, its a shopping question. These are not good questions to ask because you could easily answer them yourself if you would learn to use google. If you want to ask a design question then go right ahead. The question is equivalent to, "I don't like this kind of orange juice please find me a better brand"
• Art: I got the point. However, I attempt to respect time of others, and quite a lot of googling did not bring any results. I am not very experienced in the topic, which might make searching difficult without some hints. Hints would be great already, not necessary to give me some specific model.

Answer 1

This may give you some ideas:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Comparitor to handle negative voltages.

• R3 sets a threshold between 0 and V+. If this is too coarse add series resistors at the top and/or bottom of the pot to narrow the range of adjustment for easier adjustment.
• The trick of the circuit is to feed the non-inverting input from a potential divider, the top of which is connected to V+. In this example \$ V_A = V_+ - \frac {V_+ - V_{IN}}{2} \$ so the input voltage can range from \$ \pm V_+\$

• Art: This looks interesting. Though, this would apply additional voltage on Vin. I suppose I should figure out how the input will react on it ..
• Transistor: Edit your question to include details on the signal source and we can consider how it will be affected. Thanks for accepting my answer but if you want to "un-accept" for a day or so it may prompt a better answer.