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Input signal generation for LMH6554 in TINA

Other Parts Discussed in Thread: ADC10D1000, LMH6554, TINA-TI, ADC12D1000

Hi,

I'm using LMH6554 differential amplifier to convert single ended to differential to drive ADC10D1000 with common mode voltage of 1.25V

I've designed the DC coupled circuit as shown in Fig 6 of application note for LMH6554 http://www.ti.com/lit/an/snoa565a/snoa565a.pdf.

The input specification of single ended input is as follows,

Input signal is exponential wave.

tr= 4ns to 200ns

tf=1us to 100us

Input swing of 600mV

I'm not able to generate the input signal as per my requirements in simulation too (TINA).

Attached is the schematic of the circuit i designed.

Please help me in simulating the circuit with input signal with above characteristics.

0511.LMH6554_1.3.TSC 

 

Regards,

Amit

  •  6825.0511.LMH6554_1.3.TSCHello Amit,

    I think the easiest option is to use the step function as an input with a coupling capacitor.  The capacitor would let the step function through pretty quickly and then it would decay over a longer time period.  You can adjust the capacitor value and the internal resistance of the source to match your rise and decay times.

    Another option is that you can create an arbitrary input file and load it into TINA in the form of a WAV file.  I have not used this method, so I would have to find someone else to help you with that. 

    Regards,

    Loren

  • Hello Loren and Amith,

    You can also use the TINA-TI piece-wise linear type for your input generator to construct this rapid rise, slow decay waveform as shown:

    To do so, just enter the x and y values as text in the Signal Editor.

    For example:

    0 0
    2n 300m
    4n 0.6
    504n 0.3
    1004n 0

    However, I don't know how to make the signal repetitive.

    Regards,

    Hooman

  • Hi Loren,

    Thank you for your reply.

    I've done the simulation with the circuit you suggested, I could verify the result too.

    Can you please help me in generating arbitrary WAV file, so that I can simulate the exact input signal and verify the outputs.

    Regards,

    Amit

  • Hi Hooman and Loren,

    Thank you for your reply.

    I've generated the same signal using square wave with appropriate inputs too. 

    As I mentioned previously, I'm driving the differential outputs from LMH6554 to Vin +/- of ADC12D1000.

    In ADC12D1000 datasheet, they mentioned about Vin +/- power specification. (Attached screenshot)

    Can you please suggest me, how to check if the input specification of ADC are matching with my designed circuit?

    And also help me to simulate my circuit with arbitrary  WAV file input. 

    I'm going with the same DC coupled circuit as shown in Fig 6 in following application note 

    http://www.ti.com/lit/an/snoa565a/snoa565a.pdf.

     

    You can Email me for any queries amithk@iwavesystems.com

    Regards,

    Amit

  • Hello Amit,

     

    To create a WAV file you will need either an editor or a good knowledge of the file format.  http://en.wikipedia.org/wiki/WAV   This is not a built in feature of TINA, you will need to find a suitable editor.

    FOr the ADC inputs I think that power is not the best measurement.  If you look on page 16 the tables list the maximum input signal voltage.  It should be either 600mVppd or 800mVppd and it should be centered on the input common mode voltage of 1.25V. 

    If you are DC coupling betweent he LMH6554 and the ADC, then the VCM pin needs to be set at 1.25V and your input signal should not exceed 1.45V nor go below 1.05V.   (each otput swings 0.4Vpp to create 0.8Vpp differential). 

    Regards,

    Loren

  • Hello Amith and Loren,

    I figured out that there is a simple TINA-TI command / text that allows a piece-wise linear source to become periodic / repetitive, as shown below.

    Use REPEAT FOREVER in the beginning and ENDREPEAT at the very end, as shown.

    For your particular exponential waveform, I've used Excel to generate the x-y exponential columns of data for one cycle. Here is that file (enter your rise and fall times in cells D2 and E2 respectively):

    3617.Waveform File E2E Hooman 4_10_14.xlsx

    Here is your LMH6554 TiNA-TI file modified for this input waveform:

    1588.LMH6554 Piecewise Linear Input E2E Hooman 4_10_14.TSC

    Regards,

    Hooman

  • Hi Loren and Hooman,

    Thank you for your support and in time response :)

    I've simulated the DC coupled circuit with 1.25V VCM, and it matches the requirement of 800mVPP max specification by ADC.

    Thank you Hooman for helping in generating the input  using  piece-wise linear signal.

    Now I got much knowledge about simulating the circuit using TINA with different input specifications.

    Best Regards,

    Amit