Greetings,
I've read the datasheet for ADAU1372 and cannot find an example for a differential filter for the DACs (optionally can be configured for differential output).
Would this filter ( AD1937 datasheet) be a good place to start?
My goal here is to achieve the lowest possible noise for driving a power amplifier.
Thanks for any assistance.
Hello wctronic,
Yes, this is a good filter to use. The OP275 requires higher voltage rails but since you are running differentially the output swing will be greater than the rails for the codec. What is…
Hello wctronic,
This design looks good for CMRR. The resistors are all equal on each leg of the differential input.
If you are running the signal a long way where you really need the best CMRR then having…
Hello wctronic,
Yes, this is a good filter to use. The OP275 requires higher voltage rails but since you are running differentially the output swing will be greater than the rails for the codec. What is good about this design is that it is a single stage. What is bad is that the CMRR will not be very good because the input impedance is not equal for both signals.
If you look at Figure 10 in the ADAU1966 datasheet you will find a filter that has the same input impedance. The problem with that filter is that the output is still differential. So then you follow this with a simple unity gain differential input amp so it will be optimized for CMRR. It also buffers the filter output to prevent issues when driving heavy loads. The down side of this circuit is that it uses more parts.
Dave T
Hello wctronic,
Yes, this is a good filter to use. The OP275 requires higher voltage rails but since you are running differentially the output swing will be greater than the rails for the codec. What is good about this design is that it is a single stage. What is bad is that the CMRR will not be very good because the input impedance is not equal for both signals.
If you look at Figure 10 in the ADAU1966 datasheet you will find a filter that has the same input impedance. The problem with that filter is that the output is still differential. So then you follow this with a simple unity gain differential input amp so it will be optimized for CMRR. It also buffers the filter output to prevent issues when driving heavy loads. The down side of this circuit is that it uses more parts.
Dave T
Hi Dave, Thanks for the reply,
I was concerned about the differing input impedance affecting CMRR with the attachment I posted previously.
Attached an image of a MFB filter I've seen, will this one pose the same CMRR issues?
The application may call for a gain of up to 3x after the DAC filter. Would it be best to stick with the filter you proposed and then add the gain in the differential input amplifier?
Thanks for your help.
