Why no negative voltage in PSoCs

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Anonymous
Not applicable

 Whats the main reason for having no negative voltage in PSoC.

   

Every commercially available opamps can be fed with volatage signals varying above and below 0.But we need to feed voltage with some offset for opamps in PSoC.

   

And even with scaling down the voltage levels the required accuracy will be lost in ADC.(even with max resolution)

   

Any particular reason

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Bob_Marlowe
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OpAmps which accept negative voltages have dual power supply, ie +5V and -5V. PSoCs have only a positive voltage.

   

 

   

Bob

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ETRO_SSN583
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There are several ways of getting around this problem.

   

 

   

One is to use a simple pwm output into a diode network that can develop a negative voltage.

   

See attached.

   

 

   

Note solutions have some ripple, generally PSRR of OpAmp will take care of this. You

   

have to perform an error analysis to meet design goals.

   

 

   

Regards, Dana.

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ETRO_SSN583
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Another way is to level shift input signals so they meet single supply CM range of PSOC inputs.

   

 

   

A cheap and dirty way is this method using 2 R's attached and terminated by Vdd. Note

   

Vdd has to be accurate, if you want accurate level shifts.

   

 

   

http://electronicdesign.com/analog/use-excel-calculate-d-level-shifter-resistor-values

   

http://www.psocdeveloper.com/forums/viewtopic.php?t=3839

   

 

   

The Excel spread sheet to calc their values, attached.

   

 

   

Regards, Dana.

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ETRO_SSN583
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One last comment, the actual physical reason has to do with production

   

CMOS processes, and inability to isolate, on a single substrate, multiple

   

polarities of voltage.

   

 

   

One other solution, is the obvious, there is a ton of low cost charge pump

   

circuits from all the major vendors. Maxim, TI, NSC, Rohm, Micrel.....

   

 

   

Regards, Dana.

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Anonymous
Not applicable

Hi,

   

I have one question about the voltage used at psoc. 
I am using a active low pass filter and i need to apply a function generator on input of my circuit. I think that i can not apply a negative voltage on my psoc but when i apply only a positive voltage, the signal on output is 0 because i am using a inverter operational amplifier. I tried apply only negative voltage on my circuit and the output is only positive, that is what i need. My question is: can i use this signal on input of my circuit ? with only negative voltage ? or this is harmful for micro ?

   

Best regards, Miguel Macedo.

   

   

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ETRO_SSN583
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Pin voltages must meet Vdda >= Vpin >= Vssa. Note that range applies

   

to analog outputs of PSOC as well. There is a small deviation from this

   

in using A/D, if its input buffer is bypassed you can exceed the rails by ~ 100

   

mV.

   

 

   

You have to translate /offset input voltages into PSOC. In case on Inv Amp

   

you have to offset it as well.

   

 

   

See the earlier posted methods of handling - inputs, eg. generating offset.

   

 

   

Regards, Dana.

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