Ltspice pi filter design series#

Longer *exactly* the same, even if, in theory, they should be. Therefore the two voltages right at the opamp's inputs are no This makes a bigĭifference, because the bottom network takes V(x) as it is, no otherĪctive elements in the forward path, while V(y) goes through the Output of the opamp, and the other to the ground. While symmetrical, has two very different paths: one goes to the The opamp is meant to be a differential PI filter, and the RC network, Input is at the bottom), has an average that is below zero. One as 'x', you'll see that their difference, V(x,y) (non-inverting If you rename the node at the end of the top OR as 'y', and the bottom Parameters, their difference should be zero. The same pulses, so if all the gates and latches have the exact same It's too late for this much weirdness, but I suspect something in the tying the input to ground influences the result - various values Grounding or tying the input up, results in a convergence error deleting the connection between 1st and 2nd stage and either

Ltspice pi filter design series#

adding series R to the other stages (not the 1st) again influences the output This spells numeric problems somewhere, maybe in the model? Adding that missing 1R brings back 3.smth. Values), but at one point I added 1000R and the output wasģ.something, then through successive approximations I ended up withĩ99R giving 2.something. adding series resistors between stages changes the output (to wrong sub file).īut even then, IV settles to ~0.733, while the others at ~0.96. While IV needs startup or uic (and copying the. testing this with XVII 2019 shows slightly different behaviour, Results in a different output, but still not 2.5

changing slightly td for some of the gates (to be less symmetric)

Tripdt=30p vhigh=5 to all the gates results in the same output Tr/tf), deleting the very unneeded Nperiods, adding td=10p tau=10p relaxing a bit the timings for the sources (50p instead of 0.1p for deleting some or all of the other opamps results in different outputs Output' is the output of the 1st opamp, U1): It's late now, so I'll goīack to these tomorrow, but here are a few preliminary tests ('the Sine wave input it functions as expectedThere is some funky stuff going on in there. Time step too small initial timepoint: trouble with u2:dzslewp-instanceĭ:u2:zslewp however when I have the lm741 as an independent circuit with a Operational amplifier and the ADA4891 get the error Fatal Error: Analysis: Ive attempted to change the circuit to include a lm741 or a ADA4892 type Volt rail that is over riding the output voltage of the preceeding LTC6226. Rail voltage) to 3.18 volts it appears the LTC6226 has a pull up to the 5 To the output in voltage follower mode the voltage changes from 2.5v (1/2 AndyĬontinuing from yesterdays question Ive added Td=1p to all the TTLĬomponents and am seeing the expected operation however when I add a LTC6226 By the way, nothing in your circuit is TTL. I suggest starting with something more reasonable. Files > z_yahoo > FAQ > faq_17-2.txt It is also possible that your unusually small Td parameter (1 picosecond) may be related to the cause. Assuming that the thing you simulated didn't have any actual mistakes (e.g., missing supply voltages, wrong connections, etc.), there are several suggestions for dealing with 'timestep too small' errors in the LTspice FAQ file. The 'timestep too small' errors have plagued SPICE users for five decades. The LTC6226 has a bias current out of the input pins, which is similar to having a weak pull-up resistance. It's no surprise that connecting anything to that output pin might change its DC operating point. I think you are lucky that the output is anywhere near the middle of the operating range. There is negative feedback, but DC is blocked by C2. Did you notice that there is no DC feedback around that op-amp? Therefore, there is nothing to set that op-amp's quiescent output voltage. I'll take your first one, freq_Phase9.asc, which has four LTC6226 op-amps. Peter, which schematic are you referring to? You recently uploaded three. Peter wrote about a voltage change at the output of an LTC6226 when something was connected to its output.