Thanks for the comments everyone, a project video on this topic will be coming up soon, and I'll post the Altium design files for that project once we release the video.
Hey, Zach great content as ever ! You are the king at teaching theory about all HW. I would love to see a numeric example for an input analog channel pin impedance design for the stability of the sampling.
Hello Zach, we will use your knowledge and thank you But I had a question. Does placing the digital part in the analog power path cause interference in the analog part? For example, if we consider a power line to the circuit parts, should power be given to the digital part in beginning of the power line and then power be given to the analog part at the end of the line or vice versa?
You can share analog and digital components on the same power rail and this will form a multiport network. Because they share the same PDN it is possible that transients excited by switching logic circuits in the digital component propagate that noise to the analog component. Decoupling capacitors help reduce this problem but there will always be a little bit of noise that gets to the analog component. If the analog part requires a precision reference, and that reference is built into the component, then the power supply noise can interfere with the precision reference and this would cause inaccuracy in the analog component. This is one reason precision ADC circuits will use a precision voltage reference that is provided by its own power supply, and the analog supply pin may also be powered by its own supply.
I’d love to see a video on audio A/D’s & preamps which have to measure microvolt signals from really low level sources at essentially DC. Specifically hum isolation and the fact that at low frequencies, the return currents are diffuse. I.e. digitizing a 1 V rms signal with 100 dB of dynamic range, without hum.
Thankyou very much for the great explanation and good video. Would it be also possible, when using a single supply for VD and VA to put a ferrite bead for the isolation, or is it better to place the resistor R6 with 51 ohms? Kind regards
I don't want to generalize that the resistance should be 51 ohms. The value you should use depends on the other components that are connected to the VD net and how fast the analog supply needs to pull power during the acquisition period. 51 Ohms is small enough to not limit that particular ADC during its acquisition and sampling period. In any case, I would not recommend a ferrite unless you can prove that the ferrite will work, such as in a test board. If you had a test board with a ferrite, and you are seeing excessive noise on the digital readout, but the digital rail power is mostly clean, then you might be boosting noise into the analog rail with the ferrite's inductance and it is probably interfering with the sampling circuitry.
Hi Zack, can you make a video on BUCK-BOOST converters, it's confusing for me to find a chip that do that (confused with buck chips in digikey results...)
Love this video. I still use a low pass filter to isolate noise propagate from DPWR to APWR but if I tie Vref to APWR. Would it fine? i worry some pules generate when adc in accquition phase because they fast charge internal sampling caps and it will pollute my Vref rail. Another question is if I use opamp would the power pin of opamp be connected to APWR or DPWR ?
Thank you, You can use a dedicated supply for VREF. An LDO for APWR is an option but you have to worry about the inaccuracy in your output divider network (if present) and in temperature drift, this is why you might place a precision reference between the LDO and the VREF pin. When using DPWR, you just need to make sure the rail is properly filtered. I sometimes see ferrites used for this, which might be okay only because VREF draws DC power, I would recommend to test on your board and if the ferrite creates too much noise you can swap it for a resistor instead. About the op-amp, if the op-amp is not supplying fast pulses (square waves) then it will probably be fine to use it on either rail, just include one additional capacitor near the input pin for decoupling.
Could you add the analog input filter calculation for the next video if possible? I would like to know for example the frequencies that the low pass filter will remove and how that can affect the measurements. Thank you for your time.
Thanks for the comments everyone, a project video on this topic will be coming up soon, and I'll post the Altium design files for that project once we release the video.
Hey, Zach great content as ever !
You are the king at teaching theory about all HW. I would love to see a numeric example for an input analog channel pin impedance design for the stability of the sampling.
Hello Zach, we will use your knowledge and thank you
But I had a question.
Does placing the digital part in the analog power path cause interference in the analog part?
For example, if we consider a power line to the circuit parts,
should power be given to the digital part in beginning of the power line and then power be given to the analog part at the end of the line or vice versa?
You can share analog and digital components on the same power rail and this will form a multiport network. Because they share the same PDN it is possible that transients excited by switching logic circuits in the digital component propagate that noise to the analog component. Decoupling capacitors help reduce this problem but there will always be a little bit of noise that gets to the analog component. If the analog part requires a precision reference, and that reference is built into the component, then the power supply noise can interfere with the precision reference and this would cause inaccuracy in the analog component. This is one reason precision ADC circuits will use a precision voltage reference that is provided by its own power supply, and the analog supply pin may also be powered by its own supply.
Great work!
Thanks for the visit
I’d love to see a video on audio A/D’s & preamps which have to measure microvolt signals from really low level sources at essentially DC. Specifically hum isolation and the fact that at low frequencies, the return currents are diffuse. I.e. digitizing a 1 V rms signal with 100 dB of dynamic range, without hum.
Thankyou very much for the great explanation and good video. Would it be also possible, when using a single supply for VD and VA to put a ferrite bead for the isolation, or is it better to place the resistor R6 with 51 ohms? Kind regards
I don't want to generalize that the resistance should be 51 ohms. The value you should use depends on the other components that are connected to the VD net and how fast the analog supply needs to pull power during the acquisition period. 51 Ohms is small enough to not limit that particular ADC during its acquisition and sampling period. In any case, I would not recommend a ferrite unless you can prove that the ferrite will work, such as in a test board. If you had a test board with a ferrite, and you are seeing excessive noise on the digital readout, but the digital rail power is mostly clean, then you might be boosting noise into the analog rail with the ferrite's inductance and it is probably interfering with the sampling circuitry.
@@Zachariah-Peterson Thankkyou very much for the answer : )
Hi Zack, can you make a video on BUCK-BOOST converters, it's confusing for me to find a chip that do that (confused with buck chips in digikey results...)
Very clear and concise.
Gj
Love this video.
I still use a low pass filter to isolate noise propagate from DPWR to APWR but if I tie Vref to APWR. Would it fine? i worry some pules generate when adc in accquition phase because they fast charge internal sampling caps and it will pollute my Vref rail.
Another question is if I use opamp would the power pin of opamp be connected to APWR or DPWR ?
Thank you, You can use a dedicated supply for VREF. An LDO for APWR is an option but you have to worry about the inaccuracy in your output divider network (if present) and in temperature drift, this is why you might place a precision reference between the LDO and the VREF pin. When using DPWR, you just need to make sure the rail is properly filtered. I sometimes see ferrites used for this, which might be okay only because VREF draws DC power, I would recommend to test on your board and if the ferrite creates too much noise you can swap it for a resistor instead. About the op-amp, if the op-amp is not supplying fast pulses (square waves) then it will probably be fine to use it on either rail, just include one additional capacitor near the input pin for decoupling.
Excellent info.
Glad you think so!
Great content! Deserves more exposure
Glad you think so!
Gracias tio Zach, saca muy buenos consejos. Saludos!
Could you add the analog input filter calculation for the next video if possible? I would like to know for example the frequencies that the low pass filter will remove and how that can affect the measurements. Thank you for your time.
Here you go: ua-cam.com/video/5SMsRApsrQQ/v-deo.html
good vidéo i like
Great content as always. Please go easy on the zoom cuts as it can be very distracting as a viewer.
Nice!
❤❤
👍👍👍