Dear reader,

I have been designing neural front end architecture for collecting multiple channel neural data. Each channel/electrode is connected to a preamplifier stage for signal amplification. The outputs from the preampifiers are to be multiplexed. I am stuck with the design of analog multiplexer. Does an 8 to 1 multiplxer involves 8 transmission gates switches with outputs connected together? Any explanations or links? I have attached an image. Somebody asked me following questions and that how i replied:

1.) What do you mean by "the signal gets distorted"?
By signals getting distorted I mean their amplitude and shape is changed. I have a problem designing analog mux. I believe an 8to1 analog mux consists of 8 transmission line switches(pass gates) with their outputs combined together. Actually I am designing a 8 channel neural front end architecture. Neural signals have very low amplitudes and they are required to be amplified before being digitized. In between the neural amplifier and the ADC I have to place a mux so that I can use one ADC for all signals from 8 channels, to conserve area.  

2.) What is the signal (amplitude and frequency)?
The signal input to each pass gate (transmission line gate) is an amplified version of neural signal with amplitude 300mV to 1.3V on a 2.8V supply in 0.5um NSCU technology. Its frequency ranges from 300Hz to 5KHz.  
3.) What is the amplitude of the gate signals?
The amplitude of the gate signal is 2.5V which is higher than  Vmax of input (1.3)+threshold voltage(0.7V)=2V. It is controlling the switch only.
4.) What is the load that the 8 inputs are seeing?  Is the load connected to one input at a time or multiple inputs at a time?
The 8 outputs from neural amplifier which are to be input to mux or more specifically the 8 analog switches of mux see a very low input impedance. The analog transmission gate is made with an NMOS and a PMOS. Their source and drain terminals are shorted together. Input is applied at source with input impedance of (1/gm II 1/gm) while the output is taken at the shorted drain terminal with output impedance: (ro1 II ro2). All the output signals from analog switches are to be combined. Should I adjust aspect ratio of analog switch MOSFETS? or shall i have to design separate circuit for combining outputs correctly.
The load of this combined output is an input terminals of ADC, most probably the gate terminals which turns out to be very high impedance again.

Thanks Aron, ur T structured switch concept works! Pass gate switch seemed to be suffering from loading issues. It loaded down its input as it had poor isolation. This one seems to have much better isolation!

Flynn