CMOS switch - DC blocking cap necessary?

[tempus fugit]

Hey all;

I'm thinking of using a switch like this one
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2054/t/al, which has can
either be operated using a dual or single power supply. If I were to use it
with a single supply, I'd bias the inputs at half of the supply voltage and
using DC blocking caps on the inputs. Would they be necessary if I were
using a dual supply though? I'm thinking that a lot of audio circuits
(buffers, amplifiers, etc) need the blocking caps, but would a switch like
this one need them?

Thanks

 

[Jon Slaughter]

"tempus fugit" <toccata@quitspammingme.ciaccess.com> wrote in message
news:21d86$497cd575$d1d89efd$16126@PRIMUS.CA...

Hey all;

I'm thinking of using a switch like this one
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2054/t/al, which has can
either be operated using a dual or single power supply. If I were to use
it
with a single supply, I'd bias the inputs at half of the supply voltage
and
using DC blocking caps on the inputs. Would they be necessary if I were
using a dual supply though? I'm thinking that a lot of audio circuits
(buffers, amplifiers, etc) need the blocking caps, but would a switch like
this one need them?

No. The signal will already be biased about ground. Remember you would
connect the ground of the signal to the ground of your circuit.

Essentially you are biasing it if you think of the -V as ground, ground as V
and +V as 2V.

What your -V power supply does is actually sorta bias the whole circuit +V.
(So gnd goes to V and V goes to 2V)

I don't know which method is best though. I would imagine an additional
power supply is not worth it and introduces it's own errors as compared to a
cap.

Note though that if the audio does have any dc component it will be
transmitted(unless the device blocks it). So ultimately you will need caps
somewhere.

 

[tempus fugit]

"Jon Slaughter" <Jon_Slaughter@Hotmail.com> wrote in message
news:cv5fl.9564$pr6.2714@flpi149.ffdc.sbc.com...

"tempus fugit" <toccata@quitspammingme.ciaccess.com> wrote in message
news:21d86$497cd575$d1d89efd$16126@PRIMUS.CA...
Hey all;

I'm thinking of using a switch like this one
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2054/t/al, which has can
either be operated using a dual or single power supply. If I were to use
it
with a single supply, I'd bias the inputs at half of the supply voltage
and
using DC blocking caps on the inputs. Would they be necessary if I were
using a dual supply though? I'm thinking that a lot of audio circuits
(buffers, amplifiers, etc) need the blocking caps, but would a switch
like
this one need them?


No. The signal will already be biased about ground. Remember you would
connect the ground of the signal to the ground of your circuit.

Essentially you are biasing it if you think of the -V as ground, ground as
V
and +V as 2V.

What your -V power supply does is actually sorta bias the whole circuit
+V.
(So gnd goes to V and V goes to 2V)

I don't know which method is best though. I would imagine an additional
power supply is not worth it and introduces it's own errors as compared to
a
cap.

Note though that if the audio does have any dc component it will be
transmitted(unless the device blocks it). So ultimately you will need
caps
somewhere.

Ok thanks for that. I'm not sure which kind of supply I'll go with, but I

thought I may be able to free up some board space with the dual supply. The
other issue is that a blocking cap (and bleed resistor maybe?) might prevent
the possibility of clicks and pops being transmitted during switching.

 

[Jon Slaughter]

"tempus fugit" <toccata@quitspammingme.ciaccess.com> wrote in message
news:17efc$497d0427$d1d89efd$3430@PRIMUS.CA...

"Jon Slaughter" <Jon_Slaughter@Hotmail.com> wrote in message
news:cv5fl.9564$pr6.2714@flpi149.ffdc.sbc.com...

"tempus fugit" <toccata@quitspammingme.ciaccess.com> wrote in message
news:21d86$497cd575$d1d89efd$16126@PRIMUS.CA...
Hey all;

I'm thinking of using a switch like this one
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2054/t/al, which has can
either be operated using a dual or single power supply. If I were to
use
it
with a single supply, I'd bias the inputs at half of the supply voltage
and
using DC blocking caps on the inputs. Would they be necessary if I were
using a dual supply though? I'm thinking that a lot of audio circuits
(buffers, amplifiers, etc) need the blocking caps, but would a switch
like
this one need them?


No. The signal will already be biased about ground. Remember you would
connect the ground of the signal to the ground of your circuit.

Essentially you are biasing it if you think of the -V as ground, ground
as
V
and +V as 2V.

What your -V power supply does is actually sorta bias the whole circuit
+V.
(So gnd goes to V and V goes to 2V)

I don't know which method is best though. I would imagine an additional
power supply is not worth it and introduces it's own errors as compared
to
a
cap.

Note though that if the audio does have any dc component it will be
transmitted(unless the device blocks it). So ultimately you will need
caps
somewhere.

Ok thanks for that. I'm not sure which kind of supply I'll go with, but I
thought I may be able to free up some board space with the dual supply.
The
other issue is that a blocking cap (and bleed resistor maybe?) might
prevent
the possibility of clicks and pops being transmitted during switching.

No, They block DC and will let the high frequency through. You need a high
pass filter to block the clicks and such(assuming it is higher than audio).

If you end up with clicking from switching(not sure what your doing so I'm
guessing) then you need some way to fix it. You can either switch when the
signal amplitude is very small or don't transition the switch too fast(this
might cause other problems though).