Solution for outputting a signal of 100KHz with -2 to +2 V

[ants]

I would like to output a signal of 100KHz with -2 to +2 volts. I have looked at a 555 timer but it seems it outputs only a positive signal.

Can someone recommend a chip that will do this?

 

[keith1200rs]

Bipolar timer chip?

You could always power a 555 from +/-2V. Simply use the -2V supply instead of the 0V in all the 555 circuit connections.

Keith.

 

[IanP]

Re: Bipolar timer chip?

Try to use a capacitor on the 555's output (and a resistor as a load), it will cut-off dc and you will have a wave that is symmetrical with reference to GND ..

IanP

 

[ants]

Bipolar timer chip?

I shall try both of those. Very good ideas.

Added after 4 hours 40 minutes:

I have made up the circuit in the diagram above. With the cap added to the output I get +1.3V and -2.0V. I've tried a few different values of cap and resistor load but no luck changing this.

Any ideas?

 

[Zokol]

Re: Bipolar timer chip?

Have you tried different input voltages?

 

[ants]

Bipolar timer chip?

I just halved the voltage supply and got+0.6 and - 1.2V

Added after 46 seconds:

I'll see if i can change the input voltage now

 

[keith1200rs]

Bipolar timer chip?

The AC coupling idea will only really work with a 50:50 mark space ratio, otherwise the output will be offset.

Keith.

 

[ants]

Bipolar timer chip?

Is the 50:50 mark space ratio the duty cycle? I.e. If I have the same on and off times for the output I will get the same positive and negative output, for example +0.5V and -0.5V ?

 

[keith1200rs]

Bipolar timer chip?

Correct. What resistor/capacitor values and power supply voltage are you using?

Keith.

 

[ants]

Bipolar timer chip?

That is helpful thank you. I actually need a duty cycle of 50%. I just haven't adjusted the values for that, only frequency.

I can supply the full range of 5-15V. I want +2 to -2 output. The output will go to a potentiometer, essentially a volume control, and this to an amp.

Added after 3 minutes:

I need 100KHz, I'd actually prefer to find a duty cycle calculator and plug the numbers in to get the right cap and resistor values. I have been using this one.

https://totusterra.com/555timercalc.html

Any ideas?

 

[IanP]

Re: Bipolar timer chip?

Here is a nice trick that allows you to correct duty cycle to 50% without changing frequency:
**broken link removed**

IanP

 

[ants]

Bipolar timer chip?

I just tried adding R3 but I dont get a signal output. Is there a particular value of R3 I should use?

 

[karesz]

Bipolar timer chip?

Hi,
Refer to to the tables pls in ElDesign Article-linked from JanP...
Do you have signal output if you connect a short over R3?
K.

 

[keith1200rs]

Re: Bipolar timer chip?

Here is a nice trick that allows you to correct duty cycle to 50% without changing frequency:
/quote]

Not so much a "trick" - just page 10 of the datasheet:

www.national.com/ds/LM/LM555.pdf

I just tried adding R3 but I dont get a signal output. Is there a particular value of R3 I should use?

It would be useful if you posted all the component values you are using, including the C & R on the output.

Keith.

 

[ants]

Bipolar timer chip?

Oh I thought the link from IanP would take me to the schematic diagram, not another page. I've just realised. I do have an output if I short out R3. I am currently using c=10nF, R1=680, R2= 47, R3=47

Thanks.

Added after 2 minutes:

Ultimately I want the 50% duty cycle so I can use a cap to get a +2 to -2V output that is uniform. Those values won't give the 100KHz I need, I've changed them while trying to understand how to get the duty cycle working at 50%. This is a work in progress

 

[keith1200rs]

Bipolar timer chip?

I would suggest you decrease the capacitor to 1nF or even smaller and increase the resistors proportionally. 47 ohms is very low.

Keith.