I am trying build high precision analog front end with pga option i searched almost mostly of pga amplifier but i was not able to find a suitable ic for my project it took allot of time to get at this point and so far i am looking for TI specialist help to improvement / correction in my attached circuit diagrams for ads1259b input stage and analog signal input stage specially resistance and capacitor calculation for ads1259b input stage
these are goals which i want to achieve with this circuit
measure voltage in microvolt range using ads1259b
where my voltage input can be from 0 to +/-1000 volt dc
measure current from 0 to +/- 10 ampere dc in micro ampere range
get maximum noise free bits resolution from ads1259b
for ac current and ac volt measurement i want that in buffer section input resistors and capacitor for ads1259b have optimized values for high data sampling rate
all opamp are opa376 low noise opamp with low offset drift
i draw almost four different configuration circuit to get feed back that which will work better and which have what kind of draw backs
here two diagrams with single ended input to ads1259b
here i have question that what if i dont use buffer before 74hc4051 ic which is same way as many other multichannel adc use like ads1256 have analog multiplexer before buffer amplifier this approach simplifies my circuit diagram as well reduce manufacture cost
second question is as i am using dual supply and internal reference is bypassed with 10uF capicotor grounded with -2.5 volt rail is this correct configuration i had checked ads1259 evm diagram and it appears in this way in that circuit
third question is what would be full scale input voltage when ads1259b is driven by single ended input and what would be in case of fully differential input stage so based on this scale i can attenuate input volt using voltage divider
as i am using dual supply so i dont think that there would be any benifitt to drive adc with fully deffrential way where if i am correct according to data sheet then it is equal to +- Vref and internal vref is 2.5 volt so full scale should be +2.5 volt to -2.5 volt which dual supply single opamp circuit can drive to ads1259b input
what maximum noise free resolution is achievable circuits shown here with 2 layer pcb where botom layer is only ground plane and pcb is well designed separate analog and digital ground plane
where case no1 driven by dc battery power source like to nimh cells in series ( 2.4 volt per 2 cells) for positive and negative rail where battery low volt range will be +/-2 volts does this will work on +-2 volts supply and avss to avdd total 4 volts and what kind of performance loss is expected on these working volts rather than standred working volt
case no2 driven by dual dc battery with lm317 / lm337 regulator for +- 2.5 volt
case no3 driven by low noise linear regulator so power supply noise will not effect the adc resolution
and sorry to ask too many question in one time but i want that in reply of this post i would start working on pcb designing
second with individual buffer before pga
these two are with differential driver to ads1295 input
and with individual buffer before multiplexer