High-speed TTL ADC

Greetings,

I would like to convert the analog output of a PDB460C-AC photodetector into digital pulses. I use it to track a nearly sinusoidal signal modulation that occurs at ~200 kHz and would like to track it with at least 8 bit precision, so my sampling rate should be 100 MSPS or higher. Each bit should be fed into a separate coaxial cable, so a parallel interface is required. Importantly, the output should be TTL or TTL-compatible (VOL-max=0.8 Volts, VOH-min = 2 Volts), into a load with an input impedance of 110 ohm.

AD9012 may have solved my problem but is obsolete. Can you please suggest a non-obsolete ADC evaluation board whose output could be TTL-compatible? I've failed to find one through the parametric search engine.

 

Many thanks,

Lior

  • 0
    •  Analog Employees 
    on Jul 15, 2016 5:30 AM

    Hi Lior,

    Thank you for considering an ADC from Analog Devices. None of the ADCs I am familiar with have TTL outputs. We have several converters with parallel CMOS outputs. In these cases the output levels (VOH, VOL) depend on the output driver power supply voltage and the load.

    The two ADCs I have in mind are:

    Part# Configuration Resolution Max Sample Rate Output Driver Type ADC Output Levels
    AD9609 single 10 bit 80Msps CMOS depends on DRVDD and load
    AD9608 dual 10 bit 125Msps CMOS or LVDS depends on DRVDD and load

    The CMOS drivers are intended to drive a largely capacitive load. It is difficult to say what the levels would be when driving a 110 Ohm load.

    Is this 110 Ohm load 110 Ohms to ground?

    Also, you mentioned being interested in a "non-obsolete ADC evaluation board whose output could be TTL-compatible". Are you looking for an ADC with TTL compatible outputs, or a board with TTL compatible drivers?

    The evaluation boards for the ADCs listed above have Fairchild 74VCX162827MTDX line drivers on the outputs.

    Thanks,

    Doug

  • Thank you Doug!

    I'm looking for a board with TTL compatible drivers. That would be easier to handle than the chip alone, I think.

    Yes, the said load is 110 ohms to ground.

    Thanks again,

    Lior

  • 0
    •  Analog Employees 
    on Jul 18, 2016 10:41 PM

    Hi Lior,

    Because the load is to ground, pulling low will be no problem. It is pulling high that is the question.

    The easiest thing I can think of is to isolate the power supplies on the Fairchild 74VCX162827MTDX drivers on the board, and adjust this supply until it meets your VOH requirements. Some trace-cutting and soldering would likely be required.

    Otherwise, you could add another driver between the board and your receiver, but this sounds more complicated than the first suggestion.

    I hope your project goes well.

    Doug