Analog switch click... Will a low pass filter smooth it out?

No. The discontinuity isn't just or mainly at high frequencies. Your waveforms show a 200 mV (if I'm reading it right) DC shift between the two waveforms. No low pass filter can help that. Balancing the average level of the original input and the filter op amp output might help. You might want to look at what's happening with no signal going in at all, and make sure everything is balanced so no DC shift occurs when you switch.

-- John

Another thought occurred to me- why switch the filter input? Leave the input connected to the filter all the time, and just select the output with the analog switch - that might eliminate half your transient problems.

-- John

Not by much, as John already wrote. Leaving out the switch on the left side may help a bit but not completely because you are effectively banging the output of your circuit from the original source to one that is phase shifted.

What helps is to gradually ease over the output from the straight-through line to the filter output and back. This can, for example, be done via FETs. Since the source is an opamp-based Sallen-Key it should be low-Z so I suggest to get rid of the input side mux.

BTW the TLV2784 is a rather pricey chip for such a mundane job. Almost like using a Ferrari to go to the post office. Consider cheaper ones. The LPV324 comes to mind but that would need at least 2.7V VCC. I bet there are other cheap ones that go lower.

Hi John,

Great suggestion. I'll try that out soon. The last time I tried something similar I actually did notice a DC level shift at the output eventhough the output was AC coupled using a 1uF capacitor. However, this was using the inverting configuration. I'll try it out again using the attenuator.

I was actually interpreting the waveform shift as due to the attenuator circuit decreasing the amplitude, but then again I could be wrong. I think I can verify this with your suggestion.

Thanks! P.

Hi Joerg,

Thanks for the suggestion! I'm still getting familiar with real world opamps. I've been reading TI's Opamps for Everyone. I really don't have any price concept right now since I'm just getting free samples. But you have a point that I should start keeping it in mind because it'll eventually matter in important projects.

Thanks! P.

What is this the intent of the system, not just the switching circuit? It looks like you are inserting a phase reversal in the path. How could such a circuit NOT cause a click unless the switch was done at a zero crossing?

"PPP"

The two signal sources each feed via a pair of series resistors ( say

At the junction of each resistor pair, a JFET is fitted so it can shunt the signal to ground if biased on.

The JFETS are driven by antiphase gate ramp voltages so perform the function of pot with wiper grounded. The change over is smoothly completed in about

At that moment when both signals have equal attenuation, that attenuation should be around 3 to 4 dB. This will mean uncorrelated signals sum with little amplitude disturbance.

The JFETs may be replaced with quick acting CdS photorsistior cells driven by LEDs for low THD applications.

...... Phil

Whenever you switch in the maximum your step becomes 2.5Vpp, or whatever level you have. That is inherent to a phase inverter. You have to add a zero-detector to your circuit. A comparator clocking a D-FF situated before the switch in the data line will do that. You have to use a fast switch, so the output step is just a few millivolts. BTW, this is a pretty useless thing, if you switch both channels at the same time, since we are not able to determine absolute phase.

"Ban"

A sine wave that instatantly changes polarity, even with no actual voltage step, will still have an obvious & audible wide band discontinuity.

........ Phil

There is no discontinuity once the zero crossing circuit is added. Yes, some high frequency energy which you could show with Fourier analysis, but the noise should be greatly reduced.

Think of listening to the output of a fullwave rectifier, which would be a worse case senario. It sounds like a harmonic rich signal, not clicks.

To be more accurate, the signal is discontinuous in the first derivative.

yes.

that step in the waveform causes the click, only way to stop the click is to change amplitude more slowly, preferably at a rate lower than audible sound,

yeah, but that will do very little to reduce the click,

Bye. Jasen

It is decreasing the amplitude, but if you can see a shift in the average level, that's a DC shift. Imagine a really low pass filter attached to that signal- you'd see no sine wave, but you would still see that DC shift. A simple attenuation would have the waveform pulling in equally on both negative and positive sides, with no change in average or DC level.

-- John

Would a voltage controlled attenautor or a digital potentiometer part of an opamp feedback setup work in attenuating the levels slower? I was thinking of still using the pulse output from a retriggerable multivibrator to control the VCA or digital potentiometer. I figured with this setup I can entirely eliminate the switch. What do you think?

Thanks! P.

Hence the discontinuity in the first derivative. Still better than switching in midstream.

" Google Groper Alert"

The electronic cross fade method I outlined will not have one.

Go away - imbecile.

....... Phil