I try to use ADG704 to switch 4 photo diodes. The anodes of the diodes are connected together and to the ground. The cathodes are connected to S1 to S4. D is the output and connected to a transimpedance amplifier (AD8616). The switch is working fine if I apply a 3V signal on each input (S1-S4). However if the signal source is changed to a photo diode, I get light signals at the output of the transimpedance amplifier with and without the diode channel being selected. It seems there is a cross talk or leakage current between the switches. According to the datasheets the leakage current should be less than 0.1nA and I am sure the photo current is much larger than that. Can some one explain to me why I get signals even the photo diode is not connected?
Regarding the photo-diodes is a current source and than at the multiplexer the current flows from drain (D) to sources (S1, S2, S3 or S4), you need to have differential power supply at the multiplexer ADG704. ADG704 is only single supply operation, so you need some other like ADG1604 that is double supply.