Dear Forum members,

I am designing a hand held battery operated mixed signal device. The device will operate from +9V Alkaline battery. I am planning to use 7805 for generating +5V supply for digital section.

For analog section I need split supply I will need +5V and -5V. The analog section contains TLC2274 Rail to Rail OpAmp and PCF8591 ADC. The opAmp is quad low bias current type and is used for following analog operations.

1. Integration of signal. 1 channel.
2. Full wave precision rectification. 2 channels.
3. Amplification. 1 channel.

Now the question is whats the best way to generate -5V for this application. The obvious question can be why at all use split supply why not single supply. For the integration operation single supply is not really a good option I know about deboo integrator but dont like it much for my precision reasons.

I was planning to use ICL7660 just after 9V battery that will give me approx -8V [ considering 10mA current ]. And this -8V going to 7905 to give -5V. Is it a good idea or it is bad considering ripples of charge pump. What is the best method for this supply generation for analog section?

With transformer powered devices my usual practice has been connecting the Analog and Digital Ground planes under the ADC. but in this case since both analog as well as Digital ground are also connected at battery -ve terminal there is no need to connect AGND and DGND at ADC am I right.

Thanks & Regards,
Prahlad Purohit