W
Walter Harley
- Jan 1, 1970
- 0
I need to mute some audio. The signal is ground-referenced AC with peak
voltages around +/-2V at most, usually more like 250mV; the source impedance
is a few hundred ohms; and the load is unknown (but at least 10k).
Requirements: For marketing reasons (having to do with how the device is
installed), I don't want to put anything in series with the audio, just a
shunt. That's not an absolute requirement, though. Parts cost needs to be
kept as low as possible, while maintaining high audio quality. I need to do
this with extremely low supply current (<5uA). The only supply voltage I
have access to is a single positive voltage which could be anywhere between
7v and 18v.
My thought was to do the following. I think I need to use two MOSFETs
because if I just use one, the body diode will conduct on peaks even when
I'm not trying to mute. Can anyone see any flaws, or perhaps a better or
simpler way to do this? With values shown, muting is only 28dB, but that
may be adequate. I could also use VN3205's, with lower Rds(on), to get to
45dB or so. To do better I'd need to put something in series with the
signal.
Other solutions I considered: (1) a CD4066, but no good with signals below
Vss (=ground). (2) a PhotoMOS relay, but that's expensive and the LED takes
too much current and anyway it's just a fancy way of switching the MOSFETs.
(3) a JFET, but Rds(on) is too high.
Vin -----------o---------- Vout
(Rs~150R) |
|
|
.---||-+
| ||<-
| ||-.
| |
| | Both MOSFET's are VN0106
| | (Typ. Rds(on) is 3 ohms)
| ||-'
| ||<-
Vctrl --o---||-+
(Rs~1MEG) |
|
|
===
GND
created by Andy´s ASCII-Circuit v1.22.310103 Beta www.tech-chat.de
voltages around +/-2V at most, usually more like 250mV; the source impedance
is a few hundred ohms; and the load is unknown (but at least 10k).
Requirements: For marketing reasons (having to do with how the device is
installed), I don't want to put anything in series with the audio, just a
shunt. That's not an absolute requirement, though. Parts cost needs to be
kept as low as possible, while maintaining high audio quality. I need to do
this with extremely low supply current (<5uA). The only supply voltage I
have access to is a single positive voltage which could be anywhere between
7v and 18v.
My thought was to do the following. I think I need to use two MOSFETs
because if I just use one, the body diode will conduct on peaks even when
I'm not trying to mute. Can anyone see any flaws, or perhaps a better or
simpler way to do this? With values shown, muting is only 28dB, but that
may be adequate. I could also use VN3205's, with lower Rds(on), to get to
45dB or so. To do better I'd need to put something in series with the
signal.
Other solutions I considered: (1) a CD4066, but no good with signals below
Vss (=ground). (2) a PhotoMOS relay, but that's expensive and the LED takes
too much current and anyway it's just a fancy way of switching the MOSFETs.
(3) a JFET, but Rds(on) is too high.
Vin -----------o---------- Vout
(Rs~150R) |
|
|
.---||-+
| ||<-
| ||-.
| |
| | Both MOSFET's are VN0106
| | (Typ. Rds(on) is 3 ohms)
| ||-'
| ||<-
Vctrl --o---||-+
(Rs~1MEG) |
|
|
===
GND
created by Andy´s ASCII-Circuit v1.22.310103 Beta www.tech-chat.de