EDNE July 2012 - (Page 46)

Developing By Christian Lohner • CadenCe design systems high-Frequency integrated circuits for test and measurement A s a vendor for high-end test and measurement solutions used in mobile radios and radio communication, Rohde & Schwarz depends on the availability of proprietary ASICs delivering key functionality and performance. The IC design engineers at Rohde & Schwarz make extensive use of an Accelerated Parallel Simulator (Virtuoso-APS) package to efficiently perform the complex simulations required to meet the demanding specifications of their high-frequency circuits. and phase noise. These analysis modes are essential for the precise simulation of circuits such as low-noise frequency dividers and phase detectors and are used very intensively by Rohde & Schwarz. TRANSIENT NOISE ANALYSIS An alternative method for the noise simulation of a circuit that does not have a static DC operating point is the Transient Noise Analysis. This analysis does not require the circuit to exhibit periodic behaviour. It works by adding pseudo-random voltage and current sources with the appropriate effective value to all noise-generating components. The drawback of this approach is that it is not possible to obtain the very useful Noise Summary mentioned above. Typically, the circuit requires long simulation run times to obtain statistically meaningful results. For these reasons, the IC design engineers of Rohde & Schwarz prefer to use PNoise Analysis and almost never use Transient Noise Analysis. The low-noise frequency dividers and phase detectors developed by Rohde & Schwarz are designed to operate over a large frequency range. This leads to special challenges when the noise performance must be simulated for low-frequency signals. This arises because, in PNoise Analysis, noise contributions are only taken into account from a specified number of sidebands. Noise coming from higher frequencies than the specified multiple of the fundamental frequency will be neglected. This means that for low-frequency signals in wideband circuits, a very large The development of high-frequency circuits is very demanding, in multiple dimensions; not least, in order to meet tight time-to-market schedules, the use of efficient development systems is a must. Rohde & Schwarz’ application of this circuit simulator provides the company’s engineers with a number of unique features that allow them to obtain results in a very efficient way. PERIODIC NOISE ANALYSIS A simulation method that designers frequently use for lownoise frequency dividers and phase detectors is Periodic Noise (PNoise) Analysis. PNoise Analysis is very similar to the traditional Noise Analysis that is offered by all circuit simulators derived from the original Berkeley SPICE. However, whereas Noise Analysis simulates the circuit at a static DC operating point, PNoise Analysis simulates the circuit for a periodic state that is the result of a Periodic Steady-State (PSS) Analysis. As a consequence, frequency-translating effects such as mixing and sampling are automatically included in the results of a PNoise Analysis. PNoise Analysis can be used for all circuits with periodic behaviour. Like the traditional Noise Analysis, it offers a Noise Summary, which is a list of noise sources sorted by the magnitude of their noise contribution to the circuit output. This list makes it very easy to identify possibilities for further reducing the noise of the circuit. PNoise Analysis also offers specialised analysis modes for the jitter of the rising or falling edge of a signal and for amplitude 46 EDN EUROPE | JULY 2012 www.edn-europe.com http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE July 2012

Cover
Contents
International Rectifer
Microchip
FTDI
Masthead
Comment
International Rectifer
Pulse
Analog Devices
Digi-Key
Analog Devices
Test & Measurement
Agilent Technologies
Baker's Best
Messe München
Understand and characterize envelope-tracking power amplifiers
Digi-Key
Cover Story
Coilcraft
Digi-Key
Signal Integrity
Altera
USB 3.0 : Bringing SuperSpeed connectivity to mobile devices
Digi-Key
Developing high-frequency integrated circuits for test and measurement
Design idea
Product Roundup
Tales from the cube

EDNE July 2012