RFRF Synthesizer Settling Time Measurement: Methods and Setup
This page explains what settling time is and how to measure the settling time of an RF synthesizer. It details different methods for measuring RF synthesizer settling time, along with a sample test setup.
Let’s understand this concept, particularly in the context of a Bluetooth transceiver chip.
While Bluetooth specifications often don’t explicitly define synthesizer settling time, it’s a crucial performance parameter. Ideally, it should be around 180 µS to allow for quick switching between Bluetooth channels. As you know, Bluetooth chips typically use a total of 79 channels worldwide.
Testing the settling time from one channel to another can be challenging. To reduce the cost of running tests on all possible channel combinations, a “worst-case” scenario is often tested. This involves verifying the synthesizer settling time from channel 0 (2.402 GHz) to channel 79 (2.480 GHz).
Figure 1 (which isn’t present here, but imagine a graph!) typically depicts a synthesizer settling time curve, representing power versus time.
RF Synthesizer Settling Time Measurement Test Setup
Figure 1 (again, imagine the image!) shows a typical setup for RF Synthesizer Settling Time Measurement. There are two main measurement methods:
- Power versus Time: This method analyzes how the power level changes over time.
- Differential Phase Versus Time (i.e., frequency vs. time): This method analyzes how the frequency changes over time.
A modulation domain analyzer, as depicted in Figure 2 (which isn’t available), commonly uses the power vs. time method. This approach typically uses the power ramp increase from 10% to 90% to determine settling time between channel 0 and channel 79, or indeed, between any two channels being tested.
In the frequency versus time method, a frequency counter is used. The counter measures the time it takes for the frequency to settle when channel 0 is selected, and then repeats the measurement for channel 79. The time difference between these two settling points is then defined as the settling time between the channels.
