pxi-6229 impedance matching for digital and analog output

[cwc278]

Hello all,

I have a PXI-6229 DAQ card, and want to use the digital and analog outputs to modulate a laser. I am considering purchasing the laser but want to make sure the card can drive it. The laser has both digital and analog modulation. The digital modulation has a 200 Ohm input impedance and requires a TTL signal. The analog modulation can be configured in two ways: either with a 50 Ohm input impedance requiring 0-1V, or with a 1.2 kOhm input impedance requiring 0-5V.

Can anyone help me determine if the DAQ card could drive these loads? It seems like both output channels can provide enough current, but the concern I have is that the 50 kOhm pull-down resistor on the digital channel (according the 6229 manual) would draw all the current, instead of it going to the load. This is also a concern for the analog output channel, but I don't see any mention of a pull-down resistor in the manual.

Any insight you can provide is much appreciated!

[Brett_Percy]

Hi cwc278

Based on the PXI 6229 manual here http://www.ni.com/pdf/manuals/375204c.pdf you should be able to use the analog output to modulate your laser.

The analog output of the 6229 can drive up to 5mA, and a 1.2kOhm input resistance at 5V will sink just over 4mA.  If your modulation is based on the level rather than the frequency of the analog input then this will definitely be fine as anything less that 100% will require less current.

The digital outputs of the 6229 can drive up to 24mA, but the 200Ohm input impedance means you need 25mA.  It might work but I wouldn't choose this option

Cheers

Brett