output voltage drop in USB-6212

[Jonnas]

Hello.

I provide 1V DC to the analog input of an AOM driver in two ways:
1. Function generator
2. DAQ interface.

When I provide the voltage with the fuction generator, the AOM works fine
(the function generator output has 50Ohm resistance), but when I provide the
voltage with the DAQ interface (NI USB-6212), I measure only ~180mV that reaches the driver
and the performance of the AOM dramatically reduces. without the load, I measure naturally 1V. 
Can you explain (probably overall power limitation of the DAQ interface output)?
Second, what needs to be done in order to use the DAQ interface for 1V DC supply to the
AOM driver? 

Thanks!

[johnsold]

Most likely the AOM requires more current than the DAQ device can provide. Many DAQ analog output (AO) lines are limited to about 5 mA. At 1 V a 50 ohm source can provide 20 mA.

First, check the specs for the AOM input impedance or current requirements.

If it is more than the DAQ AO can provide, you will need a buffer amplifier which can provide enough current. We cannot suggest an amplifier without knowing the current requirements.

Lynn

[AnalogKid2DigitalMan]

The AOM's I have worked with were typically high-speed and they incorporated 50ohm inputs.

As Lynn suggested, check the specifications.

-AK2DM

[Jonnas]

Thanks.

I figured as much.

The data sheet I have doesn't specify any current consumption.

I wrote the manufacturer and will update.

The USB-6212 is limited to 2mA analog output..

J 

[Henrik_Volkers]

First: Output current!

Second: A 6212 is limited to 125kHz max output freq.  (250kHz update rate).

All AOMs I could put my hands on started somewhere in the MHz region .... 😮

IF you have a AOM in the <125kHz region ... where can find somemore specs??

So maybe you need to look for a VCO with enough power...

[Jonnas]

---

@Henrik_Volkers wrote:

First: Output current!

Second: A 6212 is limited to 125kHz max output freq.  (250kHz update rate).

All AOMs I could put my hands on started somewhere in the MHz region .... 😮

IF you have a AOM in the <125kHz region ... where can find somemore specs??

So maybe you need to look for a VCO with enough power...

---

Thanks Henrik!!

Indeed, the AOM has a fixed frequency (80MHz).

I just gor word from the manufacturer today that the driving

current is 2mA (the limit of the USB-6212).

Two questions:

1. What is "VCO"

2. The AOM can be operated with an input voltage of 1VDC.

    in that case, is there any significance to the max frequency output 

    of the DAQ?

Thanks again

-J

[crossrulz]

---

Jonnas wrote:

1. What is "VCO"

2. The AOM can be operated with an input voltage of 1VDC.

    in that case, is there any significance to the max frequency output 

    of the DAQ?

---

1. Voltage Controlled Oscillator.
2. You had to use a function generator to run the AOM before.  What frequency range were you using with that?  That is what matters when it comes to the DAQ.  The input voltage means nothing.

[Jonnas]

---

@crossrulz wrote:

---

Jonnas wrote:

1. What is "VCO"

2. The AOM can be operated with an input voltage of 1VDC.

    in that case, is there any significance to the max frequency output 

    of the DAQ?

---

1. Voltage Controlled Oscillator.
2. You had to use a function generator to run the AOM before.  What frequency range were you using with that?  That is what matters when it comes to the DAQ.  The input voltage means nothing.

---

Thanks fot the link.

I intend to (and do) use the DAQ as a DC voltage supply

(1V DC).

Even when using the function generator it was used just as a fancy

voltage supplier (that was the instrumat available for me) and supplied

1V DC.

If (and when) I'll want to use an alternating signal it'll be at  1MHz frequency max.

By input voltage I meant the input voltage to the AOM driver (1V DC according to spec)-

sorry for not being clear

-J

[Jonnas]

Ok.

So I built a uniti gain op-amp in order to provide the necessary 

amperage but still, when I connect the USB-6212-op-amp-device,

there's a voltage drop...

Could the op-amp not doing the job (suppling more current) done?

Any thuoghts?

Thanks.

-J

[LindsW]

Hi Jonnas,

It sounds like a unity gain op-amp (voltage follower) is the correct approach.  Take a look at this white paper article, which discusses how to hook up a DAQ device with a voltage follower (section 3) to double check you have it connected correctly:

http://www.ni.com/white-paper/4494/en/#toc3

Regards,