Agilent Measurement Journal - Issue 3 - 2007 - (Page 51)

W When ampliﬁers and switches are turned on, the output signal rises then settles. Measurements usually focus on rise time, which most device manufacturers will specify. In many cases, however, settling time is at least equally important and is often even more so since settling time is usually much slower than rise time. The faster an electronic circuit will settle, the faster communication can begin through the circuit. For example, faster switching increases measurement throughput, which reduces the cost of testing. It also boosts communication throughput, potentially increasing proﬁt for a service provider. Accurate measurements of settling time provide greater assurance that a device can meet customer requirements for fast switching. As an example, it may be required that the insertion loss of a switch settle to within 0.01 dB of its ﬁnal value within 350 µs. Dependable measurements will help the switch manufacturer ensure that its product can meet such a requirement. Better measurements also can enable streamlined device qualiﬁcation as well as improved system margins and yields for the end user. Practitioners use a variety of instruments and techniques to measure settling time. One common method requires an oscilloscope and a pulse generator. Two less common — but more accurate — approaches utilize a vector network analyzer (VNA). This article describes these three approaches and gives measurement examples using the VNA-based methods. Measuring settling time with an oscilloscope Using an oscilloscope and pulse generator, a DC voltage is applied to the input of the switch and a control pulse is used to close the switch (Figure 1). The scope input is applied to the output of the switch and is triggered by the control pulse. The settling time can be ascertained to within a speciﬁed range, usually in millivolts. This method has one key advantage: Rise time can be accurately measured if the scope has sufﬁcient bandwidth. Pulse generator In Control pulse DUT Scope Out Figure 1. Example measurement setup for oscilloscope method Unfortunately, this simple setup has three important shortcomings. First, it will not work with devices that have DC blocking on the input or output. Second, it cannot easily measure the frequency response of the device or account for mismatches and losses in the measurement path. Finally, measurement accuracy may be too low for many applications. The DC-blocking issue can be alleviated by using a radio frequency (RF) input instead of a DC input. Even so, this method is hampered by issues such as scope frequency response, sampling rate, memory depth and envelope processing (settling-time information is contained in the envelope of the RF signal). Each of these issues can be addressed by performing settling-time measurements using a VNA. Agilent Measurement Journal 51

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 3 - 2007

Applying Ingenuity to the Measurement of Emerging Technologies Contents Emerging Innovations Department Delivering Bigger Benefits by Optimizing Customer Workflows Measuring Material Properties at the Nanoscale Utilizing In Situ Atomic Force Microscopy in Life Science, Pharmaceutical and other Bio-Related Applications WiMAX™: Plotting a New Path to Global Mobility Addressing the Triple Complexity of Triple-Play Networks What Next for Mobile Telephony? Exploring the Inner Workings of Tire-Pressure Monitoring Systems Developing, Assessing and Applying a High-Resolution Thin-Film Magnetic Probe Making Accurate Settling-Time Measurements Using a Vector Network Analyzer Applying Metabolomics Methods to the Study of Bacterial Leaf Blight in Rice Plants Measuring Stream Dynamics with Fiber Optics survey

Agilent Measurement Journal - Issue 3 - 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.