In Part 1 I explained how to create a versatile and accurate differential source in TINA-TI which comes in handy when dealing with a fully differential amplifier (FDA) or other differential circuits. In this post, I’ll explain the procedure for importing the model of another device (non TI) into TINA-TI.
Problem: How to simulate your circuit, which may contain non-TI devices, using TINA-TI?
Solution: Import the simulation model of the non-TI devices into TINA-TI and simulate away! Let’s consider a situation you’d need to apply this technique and then work through it.
Learning by Example: You are trying to build a fast (100MHz) MFB 2nd order low pass filter (LPF) which needs a very high speed amplifier. A current feedback amplifier (CFA) is a wise choice given the speed requirement (10x the roll-off frequency rule-of-thumb) so you choose the LMH6703, a 1.2GHz bandwidth CFA. When you simulate or build the circuit you see the classic issue with a CFA where it oscillates with a capacitor in the feedback path, as shown in Figure 1:
Figure 1: A MFP LPF using LMH6703 (CFA) needs modification to function properly
You could then apply the technique outlined in Expanding the usability of current-feedback-amplifiers application note, which places a ferrite bead (Z) in series with the inverting input (see Figure 2) to:
Figure 2: Stability with minimal noise impact using ferrite bead
To help choose or simulate the right ferrite bead for the application, one could utilize TINA-TI if the ferrite bead manufacturer, such as Lairdtech Ferrite Bead Models zip, provides an electrical simulation model for the device. After choosing a bead candidate, based on its characteristics that fit the LMH6703 stability requirements, follow the steps below to import its model into TINA-TI:
1. Get the zipped beads model, unzip it, and save the unzipped model file (*.lib, many devices combined into one file) to a known directory, such as: “C:\Program Files (x86)\DesignSoft\Tina 9 - TI\SPICELIB”
2. Use TINA’s Tools, New Macro Wizard to import the Pspice model of the new device (i.e. the ferrite chip candidate) as outlined in Figure 3:
Figure 3: New Macro to Point to the right Simulation File
3. Assign a symbol and device pins to the net list, as outlined in Figure 4:
Figure 4: Symbol and Pin Assignment
4. Place the Macro on the schematic as outlined in Figure 5:
Figure 5: Locate and Place New Macro
Now the device is available for simulation on this schematic, and other ones, just like any other built-in model!
If you have chosen the right ferrite bead for the job, running transient analysis should yield a stable transient response (see Figure 6) and little or no frequency response peaking. Noise simulation is also par for the course now that you have a self-contained complete schematic.
Figure 6: Confirm stability with new macro in circuit
Have fun applying this and I look forward to exploring other TINA-TI tips and tricks we will work through together!
Until next time keep your comments and future-topic suggestions coming so that I can gauge the usefulness of this series and respond accordingly and to also guide the direction of future topics for maximum benefit to all.