How do i Model This Part in LTSpice IV? - Page 1
Forum section: electronics / beginners

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 06, 2011, 07:03:00 am
content: i want to design circuit using these Texas Instruments chips:THS3202, 2GHz, 9KV/us, ±7.5VssTHS3061, 300MHz, 7KV/us, ±15Vssbut first i have to simulate it in LTSpice IV (or any better suggestion?). since LTSpice only provide Linear Technology chips, so TI chips are not available in the library. i dont have the TI chip yet, so i dont know how they will behave. worst the above chips are "Current Feedback Operational Amplifier", which is quite new to me at least, and not behave like a normal "Voltage Feedback Amplifier".1) any links to the TI chip library that can be used in LTSpice will be appreciated.2) How do i create a new component/library in LTSpice if i have no knowledge of the real component behaviour? and the simulation output as close as the real component/circuit?thanx.

author: allanw
author_rank: Frequent Contributor
timestamp: May 06, 2011, 07:20:28 am
content: Use TI's program:http://focus.ti.com/docs/toolsw/folders/print/tina-ti.html

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 06, 2011, 07:28:07 am
content: ahh that! thanx alot! i've been browsing TI site in pain. still cant get everything right... me. what a slow server!edit: downloading the tina...... 1%...

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 06, 2011, 12:32:34 pm
content: this is cool yo! i got a new 'assy'lloscope!it seems i'm pushing the 3062 to its GBW limit.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 06, 2011, 01:10:21 pm
content: but wait. 3202 datasheet said, Vpp max = ±7.5V. i just supply it with ±12V but the sim didnt smoke it. this seems (picture) more realistic. but i wonder, 3062 seems immune to distortion even with the 10X gain (exceeded its GBW far enough). o well, we'll see in the real life.

author: allanw
author_rank: Frequent Contributor
timestamp: May 06, 2011, 01:34:46 pm
content: Did you see this? Nice warning right after the introduction section:

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 06, 2011, 03:08:30 pm
content: yes i just read that few minutes ago. i just got excited with tina earlier. i guess 3095 is the way (while stock last, 3091 is out of stock). i'm in the middle simulating 3095 right now.

author: tecman
author_rank: Frequent Contributor
timestamp: May 06, 2011, 05:51:31 pm
content: What are you doing that requires such hot (high frequency) chips. If it is audio stuff, there are a number of other ultra low distortion, standard voltage mode chips on the market.Although they are called current mode op-amps, I do not believe that they are what was called Norton amplifiers where you match, or mirror the input currents. They appear to sum, similar to a standard op-amp. Be careful, however, since the input differential voltage range for the inputs is quite small, compared to a normal op-amp.paul

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 06, 2011, 07:57:18 pm
content: Quote from: tecman on May 06, 2011, 05:51:31 pmnow i still get this question.i need an amplifier to increase the Vpp of the output of this...i will externally supply it with ±12V. allanw and others atOp Amp (uA741CN) Helphave been around guiding me.Quote from: tecman on May 06, 2011, 05:51:31 pmthe 3095 datasheet says... Differential input voltage Vid = ±4V should be ok i think. The Hantek's output is max at ±3.5V

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 06, 2011, 08:21:07 pm
content: there is in THS3095 datasheet (picture) saying the SPICE only model within the chip non-saturation region, and it will perform poorly in saturated/distorted region. maybe that explained why the THS3062 didnt distort in the above sim. there's also mentioning about small signal AC, so not sure what small is small.

author: Zero999
author_rank: Super Contributor
timestamp: May 06, 2011, 08:36:50 pm
content: I've noticed that all of the op-amps specified so far are compensated to be stable at unity gain but is this really important?If the minimum gain requirement is >1 then why not go for an uncompensated amplifier and add the required capacitance to make it stable at the desired gain?

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 06, 2011, 09:02:11 pm
content: Quote from: Hero999 on May 06, 2011, 08:36:50 pmsomeone should tell us why. i guess its easier for a layman like me to estimate the BW of an opamp from the gain required. all i have right now is reading the wiki:Frequency compensationCurrent-feedback operational amplifierGain–bandwidth productit is told that CFB opamp is much faster than VFB opamp.

author: allanw
author_rank: Frequent Contributor
timestamp: May 06, 2011, 10:54:02 pm
content: True, a de-compensated amplifier would be more useful. They are definitely less available than the unity-gain stable ones though. I don't think I've seen any at high bandwidth/slew rate.

author: Zero999
author_rank: Super Contributor
timestamp: May 07, 2011, 05:05:14 pm
content: Here are some uncompensated amplifier ICs I've found using Google. I don't know what your exact requirements are (too many threads) but hopefully one of them will do.THS4021HA-2625OPA685

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 07, 2011, 06:24:52 pm
content: thanx hero for the pointers. i will study them. this thread particularly for simulating those opamp. those opamp (topmost) are among the top "high slew rate" AND "high GBW" spec i can find (and available in ebay too, which is my "easy" shopping place). the purpose and why of that is discussed in another thread (evolved from uA741)