[sdiy] VCO tempco R locataion

[Stewart Pye]

Hi Ian,

I'm planning on using OPA2134 op amps that have a max Vio of 2mV.

I'm looking at your Sawtooth VCO design at the moment and planning on 
basing my circuit on that, but using REF02 for a 5V reference voltage, 
and possibly using the tempco resistor in the voltage divider to the 
base of the expo transistor.

Regards,
Stewart.


Ian Fritz wrote:
> At 02:01 PM 7/30/2010, JH. wrote:
>
>> In feedback loop of opamp means no such error (low impedance), but it 
>> also means the opamp's input noise appears at the transitor base 
>> without attenuation, which may or may not be a good thing, according 
>> to your desigh philosophy.
>
> Yes, and additionally the opamp offset voltage leads to a temperature 
> drift.  So it is really a good idea to spend for a high-performance 
> opamp with this method.
>
>   Ian
>