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Old 23rd May 2021, 11:42 am   #1
Hydrocarz
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Arrow Bilateral Switch!???

First, Thank you for providing this forum to me! Secondly, The experience I have had here at this forum is breath taking! You guy's are so nice and respectful here. I am most certainly joyed with how you all respectfully communicate to one another here, its very impressive to see this. I'm a founder of a forum, and those guys are something else!

I have indeed another post on this forum but please do not relate it to what I'm about to ask here, as it is related but much like the Circuit itself. I feel like I'm working on a matrix circuit and I feel like I am having to act in a matrix way to solve these riddles the aliens has left me pondering at. Here we go... Just to clear up my confusion.

A photo will be provided. Also, thank you FR for the help you've given me, I just want several opinions and really dont want to load you over. You know who you are.


The Bilateral Switch, known as the CD4066B, I will include the datasheet here for user reference purposes. and if it needs to be removed, I understand. I will also include a photo.

In the bottom left of the photo I've included, you will see 2 terminals labeled PJ2. That is a Plug harness going upward to a Display Driver PCB, it's not needed so just ignor that part.

My question is, I simply do not understand the Bilateral switch at all. I view it as a silicone relay. I dont understand if the control pins are voltage controlled. Why in the world are there 8 resistors on the control pins all different values? I simply can not for the life of me understand why they are all connected together and feeding the OP amp, or if the Op amp is somehow feeding they Bilateral switches then on the Display screen. I see that you can set all the variable resistors, but as of this moment its senseless alien smuck in my mind. I look forward to someone explaining this so I can understand it and maybe give myself a big slap on the head and say, my god thats just simple as pie! But right now, I'm in very big trouble because I can not for the life of me understand the point of this.

Thank you in advance, very much, to the one that can explain this to me!
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Old 23rd May 2021, 12:20 pm   #2
llama
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Default Re: Bilateral Op Amp!???

To my eye, those different voltage inputs are the signal voltages going through each silicon relay, the one selected going straight to the voltage-follower IC on the right of the diagram. I haven't checked on the pin numbers but each cell of the 4066 has an input at the bottom of it and this is the "on" select for the cell in question. Hope my description/sight of it is clear! Each cell is only being used in the "left-to-right" direction.
Graham
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Old 23rd May 2021, 12:45 pm   #3
Dickie
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Default Re: Bilateral Op Amp!???

I agree. The 4066 is acting like a 1-pole 8-way switch selecting 1 of 8 preset levels.
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Last edited by Dickie; 23rd May 2021 at 12:54 pm.
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Old 23rd May 2021, 1:05 pm   #4
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Default Re: Bilateral Switch!???

The design has eight different pots (each with a fixed resistor to spread its scale a bit) and these adjust the gain of a signal path, seemingly to calibrate some other changes off of the diagram.

As said, the CD4066 bilateral switches act as a single pole 8-way switch. One of the pot outputs is passed to the output end opamp, and the rest are ignored. So, it's a switched gain section, having 8 choices and each one is set by a pot to adjust the accuracy of something unseen.

The 4066 switches are each a pair of MOS transistors. One P-channel, one N-channel connected across each other. The transistors are made pretty much symmetrical so which is drain and which is source doesn't matter. to turn on the N channel transistor, the gate needs to be more positive than the channel. To turn on the P channel transistor, its gate needs to be more negative than the channel.

So the two gates need to go in opposite directions, whether the switch is turned on or off. So each switch has a simple CMOS logic inverter. One transistor gets the incoming control pin voltage, the other transistor gets it via the inverter. So both transistors are on together or off together.

The analogue signal will set the channel voltage somewhere. If it's up near the supply voltage, that's OK, the N channel transistor may not have enough gate volts to turn it on, but the P-channel one will be on just fine.

If the channel is down by ground, the N channel will be doing the business even if the P channel one can't turn on.

So as the analogue signal swings the channel voltage anywhere between ground and supply rails, one, the other or both transistors will pass the signal, looking like a smallish resistance when the switch is commanded to be on.

Either transistor will carry current in either direction if it's on (the bilateral bit) and this is due to them being symmetrical in shape on the die.

They work well, and are a brilliant idea. You can find more modern ones, blisteringly fast ones under the heading "Fast Bus Switches" fast enough to make ultra high performance frequency mixers at RF frequencies.

David

Oh, I edited the title..... anyone reading the original one would be expecting bilateral opamps, when it's the switches which are bilateral.
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Old 24th May 2021, 1:54 am   #5
Hydrocarz
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Default Re: Bilateral Switch!???

I think I understand it more now, The Trigger pins on the 4066 are routed to several other Logic chips. I can now see how the resistance is altered. I thought they was connected elsewhere with different value resistors, but those numbers are not resistor values, they are Frequency selection switches.
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