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Old 22nd May 2003, 05:15 PM   #21
sek is offline sek  Germany
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Hi,

has anyone considered TI's (BB's) MPC506/507 (16channel single ended/8 channel symmetric)?

It has "break before make" (click-free) circuitry and runs from +-15V. I guess it's thought as an alternative for the established SSMs.

I'm going to receive some soon, but it'l take a while for me to test them. So this is probably more a request than a suggestion...

Sebastian

PS: Usability of the 4066 in audio also depends on the used voltage levels, thus on the used input sources... Not that I like 4066s with low voltage levels, but I think 4066s are a no-no with higher (dynamic) levels or when you connect unknown sources (aka not build by yourself ) ...
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Old 22nd May 2003, 05:18 PM   #22
dhaen is offline dhaen  Europe
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Hi Jan,

I wasn't clear. I meant the series resistor value, compared with the "on" resistance of the switch.
It's the "on" resistance that varies of course.

Cheers,
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Old 22nd May 2003, 07:13 PM   #23
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Default mux stuff

OK John, I'm with you.

You are right. But as with many things, also here you get conflicting requirements. Making the series resistance too high gets you into noise country. As always, good engineering is the art to choose between several evils, correctly. But you know all this.

Jan Didden
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Old 22nd May 2003, 07:18 PM   #24
dhaen is offline dhaen  Europe
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Jan,

I've found the best compromise is to use the same value input resistor as feedback resistor on the opamp. The value I've settled on is 10K.
With DG211 /212 as switches and a reasonable opamp, the results are good, and the cost reasonable.

Cheers,
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Old 22nd May 2003, 07:22 PM   #25
mlloyd1 is offline mlloyd1  United States
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Default Re: mux stuff

I'm still missing it.

Let me redraw as shown below.
The input signal at Vin is the same for both.
With the same input signal to both, which switch has the most current throught it and the most voltage across it (consequently, having its Ron modulated the most)? I understand the switch at virtual ground has one end "fixed" at zero. The other switch has both ends moving, but I think the actual swing "across the switch" itself is less?

Be gentle, it's been a rough week
mlloyd1

Quote:
Originally posted by janneman
The resistance issue is a non-issue, as long as it is a constant resistance (what's 100 Ohms between friends, eh?). The resistance MODULATION is an issue, meaning the resistance varies through the signal cycle. That means distortion. The modulation comes from the voltage swing of the mux. So, fig 2, with minimal voltage swing, is the better one.

Jan Didden
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File Type: gif switch-model.gif (2.4 KB, 410 views)
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Old 22nd May 2003, 07:57 PM   #26
dhaen is offline dhaen  Europe
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Default Yes, nearly Friday....

Hi Mlloyd1,

Although I have stated that I favour circuit 2, I agree that resistance modulation is probably worse. What I've tried to get over, is that it's effects can be made so small by a careful choice of series resistor, and chosing a reasonable switch IC.
My reasons for going the circuit 2 way, are largely based on it's better crosstalk performance.


Cheers,
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Old 23rd May 2003, 03:16 AM   #27
mlloyd1 is offline mlloyd1  United States
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Default Re: Yes, nearly Friday....

dhaen:
OK. I understand what you are saying.
Can you say a bit more about your rational for crosstalk being better in circuit 2?

mlloyd1

Quote:
Originally posted by dhaen
... My reasons for going the circuit 2 way, are largely based on it's better crosstalk performance....
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Old 23rd May 2003, 07:57 AM   #28
dhaen is offline dhaen  Europe
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Default Re: Re: Yes, nearly Friday....

Quote:
Originally posted by mlloyd1
dhaen:
OK. I understand what you are saying.
Can you say a bit more about your rational for crosstalk being better in circuit 2?

mlloyd1

This is my theory:
If we say that most of the crosstalk occurs inside the analogue switch, then in circuit 1, capacitive coupling will be greater, due to the higher impedance.
My measurements have agreed with this, though I'm sure there are other factors that I've not thought of, or cannot recall.
An admission I must make, is that I was also concerned with "mixing effects". In other words, it mattered to me that Input A didn't feed back up into Input B. This was because they also fed other switches. Virtual eath systems are good at this.

Cheers,
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Old 23rd May 2003, 08:05 AM   #29
dhaen is offline dhaen  Europe
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Quote:
Originally posted by sek
Hi,

has anyone considered TI's (BB's) MPC506/507 (16channel single ended/8 channel symmetric)?

It has "break before make" (click-free) circuitry and runs from +-15V. I guess it's thought as an alternative for the established SSMs.

snip......
Hi Sebastian,

I missed your post yesterday...

I've used the '506. The performance is good. However, I moved to DG211's because the board layout is easier, and more flexibility in address decoding, for my applications.
With all these devices, I recommend running at maximum supply rails +15 -15v.

Cheers,
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Old 2nd June 2003, 11:33 AM   #30
eplpwr is offline eplpwr  Sweden
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Thumbs up My design...

Hi everybody, and thanks a lot for your input!

I've now decided to go for the "virtual ground switching"
solution, since the benefits seems to be much greater that
the disadvantages.

I'll use 10 kOhms input resistors for each input, together
with 2x1N4148 to "cut" the signals that are not selected
(found that in the SSM2404 datasheet). The RDS(on) for
the ADG406 switch seems extremely flat if it's used in the
mV range, and It'll run on +/- 18V to have the lowest
possible RDS(on).

sek: I also have two MPC506 switches to try out, but just
looking at the DS they don't seem to have the same
performance as the ADG406. (The MPC506:es are pin
compatible with the '406:es.)

Now I just have to drill the PCB...

Again, thanks everybody for your input!

/ Per
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