DAC900-Q1: Question about the output of the DAC

david schumerth

Part Number: DAC900-Q1
Other Parts Discussed in Thread: OPA354, OPA690

Tool/software:

I am trying to take the output of the DAC and convert it to voltage from 0V to 6V. I am using a non-inverting op-amp with a gain of 6 to accomplish this. I have simulated the op-amp circuit (with a current source as a stand in for the DAC) and I believe that my circuit will work, but I what I am doing is not shown in the datasheet nor in the EVM schematic.

At my last schematic review, I was given the action item of making the schematic match the app notes in the datasheet. I am trying to avoid using a negative supply rail for the op-amp, otherwise I would just add a stage before amplifying the analog signal. I tried to use the single-ended example, but replace the cable with an op-amp.

So, my question is: am I going down the wrong path with my current schematic?

6 months ago

0 Rob Reeder 6 months ago

TI__Mastermind 33360 points

Hi David,

I see you want to DC couple? Is that the case?

If so, you need to develop a network interface from the output of the DAC to the input of the amplifier.

The DAC outputs must be in compliance too. So I am not sure you can get away with a single power supply on the amplifier.

Please give me a few days to look into this for you.

Regards,

Rob

0 david schumerth 6 months ago in reply to Rob Reeder

Prodigy 20 points

Thank you for the reply.

I am trying to control an analog controlled attenuator. The attenuator, needs an analog voltage of 0Vdc to +6Vdc.

I might have misunderstood the datasheet when I saw the single ended configuration in the datasheet on page 18. I thought I could only use one of the outputs to drive an op-amp. I do think I did something wrong, so any help will be appreciated.

~David Schumerth

0 Rob Reeder 6 months ago in reply to david schumerth

TI__Mastermind 33360 points

Hi David,

It might be a good idea to send me a block diagram of what you would like to implement ultimately.

Per the datasheet, you can use a single stage opamp to DC couple to the outputs using the following configuration below.

However, you will need to use a dual power supply of the opamp. This is so the DAC output swing can go plus and minus and still be within compliance.

After this stage you can use an attenuator. If you don't need to DC couple, this makes it easier. Please advise.

Thanks,

Rob

0 david schumerth 6 months ago in reply to Rob Reeder

Prodigy 20 points

I am not sure if I need to be DC coupled. My assumption is that it will be needed, because the attenuator needs a dc voltage to control the amount of attenuation that is applied to the RF.

I have attached a block diagram and the datasheet for the attenuator.

PVVAN-6012-60-MP Outline.pdf