Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!crdgw1!ge-dab!sunny!harrison From: harrison@sunny.DAB.GE.COM (Gregory Harrison) Newsgroups: comp.dsp Subject: Re: More digital mixer stuff Message-ID: <2437@ge-dab.GE.COM> Date: 18 Oct 89 00:17:45 GMT References: <9238@pyr.gatech.EDU> <7905@microsoft.UUCP> <9247@pyr.gatech.EDU> <1845@draken.nada.kth.se> <7973@microsoft.UUCP> Sender: news@ge-dab.GE.COM Reply-To: harrison@sunny.UUCP (Gregory Harrison) Organization: GE Simulation & Control Systems Dept., Daytona Beach, FL Lines: 32 Distribution:USA In article <7973@microsoft.UUCP> brianw@microsoft.UUCP (Brian Willoughby) writes: >In article <1845@draken.nada.kth.se> d88-jwa@nada.kth.se (Jon W{tte) writes: > >>>>transitions take longer than 1 to 0 transistions. Then, for a digital >>>>sample changing from $8000 to $7FFF, you would first get $0000 on the >>>>DAC output before all the other 15 bits changed to $7FFF. Ugly and BIG >>>>spike! Analog sample and hold allows the outputs to be disconnented How about Gray Code? Apart from the p = 0.999 chance that no manufacturers currently make Gray code DACs, the advantage to this method would be less of a spike due to large numbers of bits changing simultaneously. In Gray code, only one bit changes between each successive ADU (Analog to Digital Unit) increment. OK, so that would fix the problem of large spikes on the analog ground (ahh, a separate regulated power source for the analog half of the DAC? That would go a long way towards reducing metallically coupled digital switching spikes to the analog output. The EMI switching spikes may have to be contended with by MMIC (Monolithic Microwave Integrated Circuit) device design philosophies on-chip. Again, OK, Gray code would counteract switching noise for increments of 1 in the signal, but what about increments (or decrements) not = 1. Is there a more advanced Gray code that will minimize the number of bits changing ~simultaneosly within a certain range? For instance, a second order Gray code that would minimize the number of bits that could change for an increment +/- 1 and +/- 2. Etcetera for third order.... Is there a better way, or does it all come down to parallel antennas radiating garbage to our delicate wires? Greg Harrison My opinions are not intended to express those of GE.