Analog switch question

I am trying to make an audio router board for a mixer. I have found sevreal analog switches that can do the job. I decided to use the MAX4173 Clickless Audio/Video Switch. Datasheet:

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Its only one thing that makes me wonder. This IC works from a +5V supply and is SPI controlled. The thing i have seen with other analog switches including the 4066 is that they require a dual supply to work with a audio signal with refrence to ground. In the datasheet it say the analog voltage swing may go from 0-5 volts.. So my question is this: Do i have to add a 2.5 V DC componet to the signal going into the switch so it may swing +-2.5 volts and then add a capacitor at the output to block the DC so it can be refrenced to ground again..?

Anders N. Vinje

Reply to
Anders N. Vinje
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I think you do. There is an interesting article on this very topic on the

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site under 'Electronic Switching with the AD4053' article.

I'm not sure if he suggests this because of the age of the chip used (i.e., maybe newer chips don't have this problem) or not. I'm going to be working with some of these ICs shortly for use in an effects pedalboard, so I guess I'll find out soon enough. BTW, there are other ICs out there that have much lower on resistances (don't know if this is a concern for you or not), made by Maxim and AnalogDevices, among others.

that

So

Reply to
tempus fugit

Yes you do

I understand what you mean. In the applications they show signal in/out and no reference to the signal levels, but in the absolute maximum ratings and in the electrical characteristics they state that the signal can't be lower than zero with single supply operation - and note one says that the signal will be clamped with internal diodes to within .3 volts of +V and Ground.

So, this has the same limitations that a 4066 has and you'd have to reference the signal to 1/2 V, keep it to less than 2.5 volts on either positive or negative excursion then recover the signal and ground reference it on the output of the switch.

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those that need a little - voltage can be done with a simple on board inverter.. a little 555 or the like timer can generate a square wave pulse that then be rectified for a - voltage source, just connect the Vss on that out put. you may want to use the Cmos version of the 555 if your working with a

5 volt supply , the bi-polar may have issues getting started at that voltage. to balance the voltage you could put a trimmer on the output of the inverter to select the correct - voltage to get near perfect zero output when the switch is on. just something to think about i guess!

something to think about.

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Jamie

International rectifier has an interesting solid state alternative to relays. It is a AC/DC solid state relay with a four amp 20 volt rating.

These new 20V single-pole, normally open, solid state relays utilize a HEXFET® MOSFET output switch, driven by a unique integrated photovoltaic generator circuit. The output switch is controlled by radiation from a GaAlAs light-emitting diode (LED) that is optically isolated from the photovoltaic generator. The new series is available in 6-pin DIP, 6-pin SMT, and in tape and reel.

On resistance 0.050 ohms On resistance DC only 0.015 ohms Amps 4.0 Amps DC 6.0 Input/Output isolation 4,000 volts

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Thank you. Starting to design PCB...

Anders

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Anders N. Vinje

They look good except for the 3 000 000 nS turn on time. The on resistance is wicked though.

that

So

capacitor

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Reply to
tempus fugit

Yeah, well this is only the first of its breed (that I know of). If they are only trying to get into the mechanical relay market it seems like an alternative. Hopefully the switching speeds and price will come down.

I kludged something together years ago with some surplus calculator solar arrays and four green leds powering them. It worked but the speed was nothing to brag about either, and it was bigger than a mechanical relay.

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I don't really know that much about this type of device, but I have been pointed to a few others like it. So would you still need to bias the ins/outs to use them for audio? It does seem odd that in the case of the Maxim parts, which are marketed as having use in audio switching/routing, they don't really mention anything about setting up a bias point for the audio to swing around.

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Reply to
tempus fugit

It requires that you undertand how the parts function.

Electronic design wasn't ever meant to be be easy !

Graham

Reply to
Eeyore

You might want to look into the 4051, 4052, 4053 series of CMOS analog switches. These are designed to switch bipolar signals if you provide bipolar supplies. They are really handy as line selectors since they have multiple poles in one package. They are not "clickless". If you switch on a signal and happen to hit it at peak, there will be a click, compliments of Mr. Fourier. However, I have not had problems with control signal feed-through clicks.

Note that in any analog switch design there can be some "on" distortion because the switch resistance is nonlinear. However, you can minimize this by making sure that the switch resistance is not a big part of the total resistance, such as by having it look into a high impedance input of the next stage.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Home of DaqGen, the FREEWARE signal generator

Reply to
Bob Masta

Thanks Bob. I guess it's kind of a toss up - which is more of a pain, biasing the ins/outs at the midpoint of the supply, or provding a bipolar supply. If I understand your comments about switching noise, you are saying that with no signal present there are no clicks, but (as one would expect) if there is a signal you will get a click because of the change in volume? From your remarks about on resistance and distortion, it follows that the loser the Ron the better?

Thanks

that

So

capacitor

Reply to
tempus fugit

The IRF gizmo is designed to replace an electromechanical relay directly and doesn't require the negative supply. They (and I) use(d) a series of small solar cells (photovoltaic array) that are lit by leds - since they can add (in series) solar cells and get any voltage they want so it is easy to come up with the 4-5 volts required by the mosfets.

Mosfets only require a few nano amps to turn them on but at high turn on voltage ~4-5 volts for saturation. Just as easy to develop a separate array to turn on each internal mosfet. So you could use them to switch audio or AC signals if the turn on/off delay isn't going to hurt your application. With a 4 amp 20 volt rating they were developed for power switching applications like relays.

For that matter, if speed isn't an issue, you could use DIP style electromechanical relays yourself.

The advantages of the cmos switches are: lots of them in a small package, and able to switch at relatively high speeds, low current consumption. Disadvantages are the high contact resistance, inability to handle voltages over/under the supply rails, low power switching ability.

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Correct.

Well, basically true, but in reality it's the nonlinearity of Ron that is the issue here. I guess if Ron were low enough compared to your load, the nonlinearity could be ignored. But in my experience there are always other issues. I recall deciding never to bother trying another 4066, despite its low Ron, in favor of the 4016, which always seemed to behave better in my circuits... though it's been a few years and I can't recall the details now. (Sorry!) But the distortion issue wasn't ever a big problem, as I recall, no matter which switch I used.

(Note that in really critical work you can often cancel distortion by running a second switch to provide an opposite distortion.)

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Reply to
Bob Masta

Hmmm... interesting about the lower Ron of the 4066 vs. 4016. I guess I'll just have to order a few different things up and see which works the best for my application. The parts I'm looking at have an Ron of 5 - 10 ohms (for the DIP) and some of the SMDs are 0.3 - 0.5. I'll probably start with the DIPs since they're easier to experiment with.

Thanks again Bob.

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Reply to
tempus fugit

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