5. Appending Other Data to the Waveform

Our 48-bit example introduced the data continuity issue, which frequently confuses first-time AWG users. A conventional signal generator creates seamless repetitions of basic waveshapes, but modulated read channel waveforms are not basic waveshapes! If the application is the repetitive generation of a phase continuous data pattern, then you need to plan your waveform editing with this in mind. If you already have several arbitrary waveforms that you need to concatenate, you might be lucky enough to find that they seamlessly connect. But you will probably get better results by stringing together the original data patterns and then convolving the longer pattern with the transition pulse response. A typical application might be to string together a preamble pattern, address and other sync patterns, and sector data patterns before the convolution step.

 

 

Figure 9. Memory requirements to simulate an entire track of data can be overwhelming!

Keep in mind that irrespective of the method of creating a waveform, AWG memory size will ultimately limit the length or size of an arbitrary waveform. The desire to completely simulate the waveform from a full disk drive revolution must be carefully evaluated. For example, running at the 1 GS/s sample rate on a 5400 RPM drive, one revolution requires a memory size of about 11 million points (11 MS), exceeding the capacity of any AWG currently available. The AWG 2041 provides only up to 4 MS, so you could simulate less than half a revolution. On the other hand, if you dropped back to a 300 MS/s sample rate, you could simulate the entire track (Figure 9).