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Simulation problems for LMH6554
I am trying to use the LMH6554 in my design. But there are some errors when doing the Pspice simulation.
I download the Pspice file of LMH6554 from National Semiconductor website, then generate the Pspice model. But when i complete the simulation schematic and start the simulation ,there are some error messages promoted:
**** INCLUDING SCHEMATIC1.net ***** source LMH6554_SIMR_R1 N00370 N00309 200 R_R3 N01387 N00370 191 R_R2 N00447 N00420 200 R_R5 0 N01387 27.7 R_R7 N02776 N02672 100 R_R4 N01220 N00447 191 X_U1 N00128 N00128 N00214 N00214 N00447 N00370 N02672 N02776 N00309+ N00420 0 N02248 LMH6554 V_V1 N00128 0 2.5VdcR_R6 0 N01220 62 V_V3 N02248 0 2.5VdcV_V2 0 N00214 2.5VdcV_V4 N01220 0 +SIN 0V 0.25V 10meg 0 0 0**** RESUMING LMH6554_Trans.cir ****.ENDUnable to find index file LMH6554.ind for library file LMH6554.libMaking new index file LMH6554.ind for library file LMH6554.libIndex has 6 entries from 1 file(s).ERROR -- Less than 2 connections at node X_U1.a0185ERROR -- Less than 2 connections at node X_U1.a0274ERROR -- Less than 2 connections at node X_U1.a0178ERROR -- Less than 2 connections at node X_U1.a0127
I don't know why...So, please help me. Thanks
I have asked an expert to look into your problem.
In the meantime, you could try to run a TINA simulation using the LMH6554 simulation file (which I'll attach to my next posting) to make sure that at least TINA works for you. As you may know, the LMH6554 pspice macromodel (an all former National Semiconductor devices) are now included in the TINA library.
Here is the LMH6554 TINA simulation file for you to try.
0876.LMH6554 SE to Diff ADC Driver 2_22_12.zip
Our expert has looked at the LMH6554 Pspice Macromodel and has been able to successfully run it with Allegro 16.3....
If you want us to look some more into this, please attach the entire circuit so that we can take a look.
Thanks for the reply.
I use the Orcad10.5 as the simulator. The schematic is attached as image and the LMH6554 Pspice model used is also attached. The simulation cannot keep going because of the error previously mentioned. Please take a look at it, to confirm the problem source, the schematic or pspice model?.. 7380.Simulation.rar
I installed the Tina-TI, and import the schematic you posted. And I can do the simulation with Tina-TI which is a very fancy modulator.
And I am not so familiar with the high speed amplifier design, actually this is the first time. May you help to exam my design? Thanks.
The schematic is:
I am using the LHM6554 as an ADC driver to convert the single end input to the differential style and drive a 5GSps ADC. My design demands :
1. Single end signal DC coupled into the Vin+ of the LMH6554, and the DC level of the signal is about 0V.
2. I want to add some DC bias(using a DAC) to Vin- of the LMH6554 to adjust the DC level of the VOD (output differential signal).
3. The VCM driven by the ADC is about 1.6Volts, What value of power supplies should I use...Because in the simulation file you attached, when the VCM is 1.25Volts the VCC is 3.75V and VSS is -1.25V. I don't know why...
are the demands can be realized by the schematic posted upon? and the Tina-TI simulation file is also attached.
0410.LMH6554 SE to Diff ADC Driver modified.rar
We are trying to look into the Orcad file you attached to see if we find any issues. I'll keep you posted.
Regarding the circuit you attached for LMH6554 in TINA:
If you need the LMH6554 to be DC coupled to the ADC with VCM= 1.6V, you'd get the best performance from the driver if the LMH6554 supplies are centered around this VCM voltage (i.e. V- = -0.9V, V+=4.1V, just like you had set it in your file). This ensures the best possible distortion and bandwidth response. If you are able to AC couple to the ADC input(s), then you could easily set the LMH6554 output CM to V+/2 (i.e. 2.5V if V+=5V, V-= ground) and you won't need the negative supply voltage. Here is more information on LMH6554 as ADC driver: http://www.ti.com/lit/an/snoa565/snoa565.pdf
The way you have arranged Vbias to be the DAC output to control the differential output offset works Ok. I don't see any issues with that. If you want this adjustment to be of either polarity (either positive or negative), you could purposely have some current sunk from the inverting input so that the DAC positive voltage output can result in bipolar differential output offset. If you are interested to see this implemented, let me know and I'll send you an example.
About your original question related to errors with LMH6554 simulation in Orcad:
We have not been able to duplicate any of your Orcad errors (we use Allegro 16.3). These simulators cannot be much different, we think. For testing purposes, please try running the attached net-list directly (open -> select Circuit Files in Pulldown) and see if runs without errors?
You may need to modify the .LIB file line to explicitly point to the .LIB file you are using. Please try both the original .MOD and the generated .LIB files. If the netlist runs without errors – then it is not a simulator/PSPICE/Orcad compatibility issue. Most likely it is a Model Editor issue.
If the net-list chokes-up with the same errors – then it is a compatibility issue – probably due to the sub-circuits in the model or the use of node zero in the model.
Here is another suggestion from my Allegro expert about your circuit / attachment that I've copied exactly for your review:
"He ran the MOD file through the Model Editor. The LMH6554 model contains it’s own sub-circuits - which get broken out into separate parts. This may also be an issue…but I would expect more errors if parts of the model were missing. He can try adding the model to the “Configuration Files –> Library” section of the Simulation Settings to make sure it sees the full model."
Here is the net-list attachment.
I have tried your suggestions, and it is not work, the errors are still there.
If the TINA-TI functions as the same as the PSPICE, i just give up using Orcad for the simulation purpose.
And I am interested in the offset shift of differential signal when using the LMH6554 (DC coupled all the way). Please send me an example design.
Finally, thank you sincerely.
Hopefully TINA should be able to provide you the same functionality as your simulation program.
I've attached a circuit which pumps just the right amount of current into the non-inverting side so that the output offset is zero when Vbias =0.25V. This allows you to provide both positive and negative output offset (+/- 0.22V) by varying Vbias (range from 0V to 0.5V). The inductor L_Current is there so that the circuit's AC characteristics are not modified and the current through R_current is DC only for the purpose of offset shifting. L_Current may or may not be needed in your application and the value I've chosen is for AC blocking purposes and may not be realistic for your application.
6087.LMH6554 SE to Diff ADC Driver with DC Offset 3_15_12.zip
I have to say, there is no -0.9V LDO regulator available in market... So, the V+=4.1V, V-=-0.9V configuration can not be achieved :(
Here is a crude method to generate a -1.1V supply for the VEE of LMH6554 from a negative supply voltage (e.g. -5V in this case):
The zener diode is from Vishay (TZS4678, 1.8V):
I have not optimized the value of R1 or T1 PNP for load regulation. I have not checked the temperature performance either (but the LMH6554 VEE is not very sensitive to variations with temperature).
Hope this helps.
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