For Gen3 systems, there are two new (6/03) functions that can provide significant performance improvements to the RI7100A platform. They are "Fast Settle" and "Frequency Offset". They both take their effect by changing the software control of the Tester's synthesizers.
Fast Settle is an attribute of any Source in the system that changes the default settling time from the "Magnitude and Phase" settling time to the "Magnitude Only" settling time. In general a source takes longer to stablilize it's phase than it's amplitude after a frequency move. If the phase is not critical, then the application designer can take advantage of the shorter time. This is the fundamental concept behind the "Fast Settle" Function. Typically the full settling time of a source can be up to 45 mSec, while the magnitude only settling is approximately 15 mSec. Care must be taken in the use of this function because it can affect RF Voltage measurements.
The following graphs show the results of magnitude and phase, with fast settling on and fast settling off. The graphs start after the tester's settling time and measure for approximately 50 ms. With fast settle off, note that the amplitude is completely settled and stable. The phase, however, is still settling.
The majority of measurements are scalar (amplitude only). For these measurements, if the test uses multiple frequencies, fast settle can improve test time. However, there are a couple of points to remember:
- All the sources involved must be set to Fast Settle. Particularly important is the receiver's local oscillator (RecLO).
- When measuring, the proper measurement must be chosen. It is common to perform a vector measurement (such as 'Measure Voltage'), then extract the amplitude. If averaging, the changing phase will cause the vector averaged amplitude to be wrong. Therefore, always choose a scalar measurement (such as 'Measure Power') when using fast settle.
Frequency Offset takes advantage of the Source architecture to make small frequency moves extremely quickly. In general terms, the synthesizer has a coarse loop and a fine loop that combine to create the frequency of interest. The coarse loop gets to roughly 10 MHz of the desired frequency, and the fine loop gets there exactly. The architecture of the fine loop allows switching in sub 1 msec, actually less than the measurement overhead. So it takes "no time" in the measurement sequence. The fine loop has an 18 MHz range. This capability dramatically changes the measurement time for "In Channel" measurements such as ACPR, IP3, power in a bandwidth, etc. These in channel measurement typically require several receiver frequency moves within a few MHz. For instance an CDMA ACPr measurement for upper and lower, adjacent and alternate channels goes from -880kHz to + 880 kHz. This is easlily implemented with Frequency offset.