Suggestions for Signal Conditioning Circuits

[kumarharsh]

I have designed two signal conditioning circuits. One is for giving input to ADC and other one is for taking output from DAC. Input to ADC signal conditioning circuit is 0-5V or 0-12V and getting an output from it in range of 0-3.3V. Similarly, DAC signal conditioning circuit is changing voltage level from 0-3.3V to 0-5V or 0-12V as per the requirement. I have given ADC input protections and all other things as per my knowledge and research. Kindly suggest any loopholes if you guys find any. I am attaching my signal conditioning circuit schematics. All the suggestions and fault point-outs are highly appreciated. Thank You.
View attachment Verification_for_signal_cond.pdf

- - - Updated - - -

Correction: I have used LT1014 in place of OP11d (Op-amp).

 

[kumarharsh]

I am attaching this as I find that some users find problem opening inline attached pdf.

 

[FvM]

I have two comments.
1. I would consider one non-inverting amplifier instead of two inverting stages.
2. The ADC protection circuit isn't safe.

 

[kumarharsh]

@FvM What are your suggestions for protecting ADC inputs? Should I also add RC anti-aliasing circuit with those clamping diodes?

 

[KlausST]

Hi,

I allways recommend an LPF to avoid/reduce alias effects and reduce noise.

Regarding protection: I don't like the idea to short circuit the output of an Opamp.
* High current,
* maybe high temperature,
* maybe crosstalk the "short circuit" situation to the other channels via the power supplies....
* and worst of all: bringing the Opamp out of regulation .... overdiriving input and output stages, maybe even latch up
can be expected.
--> the use of a series resistor may prevent all this.

Some ADC have switched capacitors (sample and hold circuit) as input. This could cause ringing at the Opamp output. --> erroneous ADC reading may occur.
An RC to the ADC may help.

We see 8 + 8 (hopefully) identical circuits, but ADCs and DACs are missing..

The signal names are misleading: I assume
* signals ADCx are not connected to the ADC
* signals DACx are not connected to the DACs

Note: At the DAC circuit .... as soon as the jumper is pulled off the output will saturate at either supply rail. On audio signals this will cause a huge "plopp" maybe distroying the power amplifier or the speakers.
I'd rather calculate one fixed resistor for your desired "high gain" and use a [jumper in series with a resistor] in parallel to the fixed resistor to select low gain.

Even with the DAC circuit I recommend to use a RC LPF....to avoid ringing. In case of audio signals I recommend to use a true reconstruction filter.

Klaus

Added
In case the analog signals enter/leave the PCB you also should consider ESD protection and EMC filters.

 

[FvM]

Used ADC isn't mentioned, hence we can't determine the exact requirements for safe protection circuit. Generally you need to
1. keep the maximum input current specification of internal protection diodes, e.g. 10 mA and
2. avoid forward biasing of internal protection diodes in a multichannel ADC, otherwise massive crosstalk may occur

Anti aliasing filter is a different topic und and completely dependent on application requirements.