Video switch - which chip to use?

Please excuse my very basic/non-existent electronics knowledge.

I am trying to build an audio/video switch which supports analogue RGBHV video up to 480p/60 (640x480) resolution, to switch a possibly large number of input devices (maybe up to 10). This is a one-off project, so I am looking for through-hole components that I can easily put together with stripboard.

From browsing through lots of components I found the ADG451 which the datasheet lists audio/video switching as an application. Is this chip suitable for my requirements? Is it overkill? I noticed there are also lower-specced versions (ADG43x, ADG41x). I would rather pay for more expensive chips since I want very little quality degradation, no noticeable noise or ghosting.

Also I need to confirm if I've got the right idea about how this would work. So from what I understand, say I have a signal input (e.g. red colour channel) from N different devices, each connected to a source terminal on N separate ADG4xx chips. The sink terminals would all be connected to the same output line, and one of the chips would be selected, say by a rotary switch, which would select the right input to connect to the output. I've heard this is called a "bus switch". Would this work with the ADG4xx chips or have I got completely the wrong idea about what these things do?

Also I'm a little bit confused about how to connect up Vss, Vdd, VL. My best guess is that Vss is connected to GND and Vdd and VL are both connected to +5V. I will be using a single 5V power supply.

One last question. I want to use a rotary switch to select the input. I think I would need the ADG452 variant since I want it to switch on when the input is high (the switch would connect +5V to the input switch, and disconnect it when not selected). Am I right?


  • 0
    •  Analog Employees 
    on May 24, 2012 3:21 PM over 8 years ago

    Hi,Apologies for late response - this one slipped through the cracks.

    480p (640x480) requires a switch or mux with about 40MHz bandwidth to ensure 0.5dB gain flatness.

    For Audio;  Low ON resistance is important to ensure that the losses are kept to a minimum in the signal chain. Also the distortion introduced by a switch is a function of the flatness of its ON resistance profile. The contribution of the ON resistance flatness in the overall distortion figure may increase significantly for low load impedances such as speakers or headphones. 

    We have a large number of 5V parts (which is sufficient for 2.5Vpp video signal and audio in 0V-5V range) with low Ron and -3dB of 40MHz or higher, depending on configuration needs.

    The ADG451 has a -3dB BW of about 100MHz with supplies of Vdd=15V, Vss=-15V.  The BW will be much lower at Vdd=5V, Vss=0V single supply.

    The 5V ADG728/9; 8:1 mux/diff 4:1 with I2C has 65MHx -3dB BW and Ron of 2.5ohms would be suitable.  So if need to switch say 4 different R inputs to one output you would connect all R inputs to Switch A inputs, connect G to mux B inputs and so on.....


    For different gain flatness spec requirements see AN-945 which explains relationship to bandwidth.

    Other related material.