analog multiplexer for high dynamic range

[Mazi3]

hi,

we have problems with analog multiplexer (dg406), becouse of crosstalk between chanels. at the imput, there are lf358 operation amplifiers, but they are disturbed with "parasitic switch" inside multiplexer which one short circuit input to negative voltage at channel change.

we solve some this using 1k resistor in series with opamp output. but this system is designed for 16bit data acquisition, which has 90+dB dynamic range. the multiplexer has only 70 dB crosstalk isolation. this is 16 channels system.

is there any better multiplexer? any layout guidelines? or is it better to use ADC with internal mux? becouse to have ADC on every chanel it become too costly

Regards!

 

[power-twq]

I suggest you use a ADC that integrate analog switch inside,

then the parasitic will be lower than PCB.

please visit

www.maxim-ic.com to find them


best regards

hi,

we have problems with analog multiplexer (dg406), becouse of crosstalk between chanels. at the imput, there are lf358 operation amplifiers, but they are disturbed with "parasitic switch" inside multiplexer which one short circuit input to negative voltage at channel change.

we solve some this using 1k resistor in series with opamp output. but this system is designed for 16bit data acquisition, which has 90+dB dynamic range. the multiplexer has only 70 dB crosstalk isolation. this is 16 channels system.

is there any better multiplexer? any layout guidelines? or is it better to use ADC with internal mux? becouse to have ADC on every chanel it become too costly

Regards!

 

[Mazi3]

hi!

i've checked the maxims adcs, but they only have multichanel sigma delta converters. they are too slow (both the sampling frequency and the processing delay). we need about 10kHz per chanel. currently we have "pulsar" family adc on board. the first layout is not very good, there is about 100 quants of crosstalk. (7 bits!!!). TI adcs are also not appropriate becouse of ther poorer performance

 

[Mazi3]

I found the ADC:

linear's LTC1859. If anyone search for similar thing