Need advice on selecting 1pps mux/switch

Hi HS,

Most multiplexers/analog switches don't care too much about duty cycle, when the frequency is ~1Hz, and your duty cycle at 1% still provides a pretty long "hi - time". That being said, if the rise time of the 1pps signal is low, so it has a fast rise time, some of that information may be distorted slightly due the parasitic capacitance of the part, but at 10ms - 100ms for your pulse width, I don't think it should should cause too much issue.

For this application this is what you need to consider:

1. Bandwidth / Switch Frequency: This is the typical -3 dB bandwidth of the switch, but capacitive  loads will degrade this figure. For more information on the bandwidth spec please see this video here

2. Timing Specifications: These specs will give you timing considerations such as transition time, enable time, disable time, and other timing parameters. This spec is usually where the duty cycle comes to play, because if the min duty cycle is below the min on-time / off-time, the signal will be ignored. The harmonic make up of different duty cycles also can cause some higher frequency spectral content that may be attenuated/distorted. But at the length of your signals I doubt this will be a huge concern, unless you need very fine resolution on all parts of the pulse.

One note, at TI the difference between a Multiplexer and a Switch is the configuration, they use the same switch architectures regardless if it is a Multiplexer or Switch. We just call anything that is 1:1 or 2:1 a switch, and any higher configuration is a Mux, but besides the naming and configuration there isn't much difference between them. 

As for digital switches versus analog switches: 

A digital switch is composed completely of logic gates and/or digital buffers. This means that if you have a 5V system, and the minimum "hi-level" input is 2.8V let say, and you get a 3.2V input, the output of the switch will be Approximately 5V because it is being supplied directly from the power source.  See below for a digital mux/switch schematic:

Dx are inputs, and S0 is the select pin. They are typically unidirectional, and they output 2 voltages, hi (1) and lo (0). 

Analog Switches can be shown below:

This shows an analog switch using a transmission gate topology, for more information about the different architectures of analog switches please see here. The biggest difference is that an analog switch creates a low impedance pathway between the source / drain which will pass a voltage through the switch. It can pass a range of voltages instead of two "logic levels". They still have digital inputs for the select pins however. 

I think we will have a part for your application, but what  is the signal range you are trying to pass, or is it a digital signal that you are passing? 

What are the power supplies looking like for your application? 

Best,

Parker Dodson

Hello, Mr Dodson.

Thank you for your reply.

The time period of 1pps is  1s due to its characteristic.

I wanna say 1pps is digital signal and the level would be 3.3V.

What would be the best part for four 1pps signals as input and one output?

Thank you