Dear all, I'm using freq_meter component from ahdlLib
to calculate instantaneous frequency of an oscillator. While doing
Spectre simulation, I'm getting the error as ========================================================== Error found by spectre at time = 20.6089 ns during transient analysis `tran'. Signal FF(FREQ_OUT) = 2.18688 GHz exceeds the blowup limit for the quantity `FF' which is (1 GHz). It is likely that the circuit is unstable. If you really want signals this large, set the `blowup' parameter of this quantity to a larger value. ========================================================== Please let me know how to resolve this issue.
Take a copy of the freq_meter model, and change the section at the top which creates a nature Frequency to the following:nature Frequency abstol = 1; access = FF; blowup = 1e12; units = "Hz";endnatureThe default blowup is 1G, which is a little small if you're measuring frequencies around 1GHz. Note I also increased abstol, since the accuracy requirements shouldn't be so tight if you have GHz signals. Even 1 might be a bit small (normal practice is to set abstol to a millionth of a typical signal level).Regards,Andrew.
Hi,I normally find no fault with Andrew's contributions, but I would like to point out that propagating an altered copy of a quasi-standard device from a common library can cause problems if you ever share your schematic with others that don't have access to where you placed the altered copy. Fortunately, there is another solution which avoids this problem!Here's the steps:1. Create a small text file that contains the following lines. simulator lang=spectre
defineLrgFreq quantity \ name="FF" \ units="Hz" \ abstol=1e-3 \ description="Frequency in Hz" \ huge=100e92. Save the file with a name like "frequency_nature.scs" in a path that would be accessible to anyone that may end up using your schematic.3. In ADE, do Setup->Simulation Files... Add the path of the file in Include Path and the name of the file in Defintion Files.Now, just leave the freq_meter as is and referenced from the standard ahdlLib. Netlist and Run will produce a netlist that lets the freq_meter operate at a higher frequency! Then save a state so that others can recall it and get your modification included already.
My practice is to make a local library for the modified elements from bmslib.. and any new ones I create.. so my first step in making a mod is to copy from bmslib to my local (corporate) lib and make the changes.. so if they instantiate from the standard lib they get the standard one, otherwise they the the corporate verilog-A/AMS block.(which is, of course, under revision control) jbd