schehrazi wrote on Mar 16th, 2007, 11:02am:Results of shooting and flexible balance with QPSS match well.
Does HB simulation have a fundamental limit when there are multiple inputs? or the accuracy can be improved some way?
I don't believe Cadence HB has a limit to the number of input but the more inputs you have, the more memory you will require to handle all the mixing products etc. If you have a large circuit you could quickly run out of memory with a large number of input tones. I generally have not had to use more than three inputs
The accuracy of the HB simulation depends on a number of factors
1. The order of harmonics of your input tones - the more the better but the slower the sim
- if you have squarish looking signal (say on an LO port of a mixer) you will need more harmonics to get good accuarcy
2. The order of the intermod products - again the more the better but the slower the sim
- cadence default is to calculate all intermods but you can select diamond rule and limit the number of intermods
3. Oversampling ratio can affect accuracy some as well - usually an OSR of 2 or 4 will suffice but will slow down the sim compared to 1
Unfortunately there is no golden rule about what order to use for your harmonics and intermod. It highly depends on your circuit, signals, and which tone you are interested in. (ie if you are only interested in the fundamental output you probably don't need that much accuracy but if you are interested in the intermods (IP2or3) then you need higher accuarcy.)