In consumer wireless, military communications, or radar, you face an ongoing bandwidth crunch in a spectrum that is filled with interference. Testing your devices via signal simulation is critical. Signal generators provide precise, highly stable test signals for a variety of components and system test applications. Knowing the capabilities and performance of your signal generators is the first step to making accurate and consistent measurements. In this two-part Application Note, we discuss the best practices to optimize your signal generator.
Table of content
1. Increase Amplitude Accuracy
RF signal generators test RF components, receivers, transmitters, and systems. A wide output power range is required for a variety of applications. The output power range of signal generators is determined by the step attenuator which comprises different combinations of attenuators and the automatic leveling control (ALC) circuit as shown in Figure 1.1. The step attenuator provides coarse power attenuation (in 5 dB steps) to achieve low power levels, and the ALC circuit is used to provide fine power level adjustment within the attenuator hold range. Signal generators offer very accurate amplitude levels at their RF output port.
In a common test setup, you are likely to use passive devices such as cables, filters, or switches, and active devices such as amplifiers or mixers between your signal generator and the device under test (DUT).
These additional components cause insertion losses or gains to the test system. You need to consider these factors and ensure an accurate amplitude level at the input to your DUT.
In addition, RF signal generators can output as high as 25 dBm and as low as -120 dBm. If you need to go beyond the specified range, you can use an amplifier to increase the output power or an attenuator to decrease it. There are several ways to optimize amplitude accuracy while you use an external amplifier, an attenuator, or other passive accessories with a signal generator. The commonly used method is to use a vector network analyzer (VNA) to measure the gain or loss of the entire signal path and enter correction values into the signal generator. Read on to learn the best practices for improving amplitude accuracy using the built-in capabilities of new signal generators.
BEST PRACTICE 1: Use Flatness Correction
When you add components between the signal generator and the DUT, the calibration plane and test plane are not on the same plane. You must correct the difference between the two planes. User flatness correction allows the digital adjustment of RF output amplitude to compensate for external losses in cables, switches, or other devices. By using a power meter and sensor to calibrate the measurement system, a table of power level corrections can automatically be created.
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