RF Design

SpectreRF AppNotes and Tutorials....Still One of our Best Kept Secrets!

Tawna — Mon, 16 Jan 2012 23:25:00 GMT

Some of you may remember the blog written several years ago " Shhhhh...SpectreRF Tutorials and AppNotes - One of Our Best Kept Secrets ". Well, the more things change...the more things stay the same! The location of these tutorials and appNotes...(read more)

Nport Application Note has been Updated and Re-Released

Tawna — Tue, 03 Jan 2012 14:00:00 GMT

Happy New Year! After many requests, I set aside some time and updated the Using the nport in Spectre and SpectreRF Simulations appNote for MMSIM 11.1. You may download the appNote on Cadence Online Support . More nport enhancements are planned, so stay...(read more)

Guidelines for Maximizing Speed vs Accuracy for Harmonic Balance - Part 2

Tawna — Tue, 01 Nov 2011 23:00:00 GMT

I am often asked for guidelines on maximizing speed vs. accuracy for SpectreRF harmonic balance simulations . Today, I'll discuss part 2 of the 3 part series consisting of: Which Engine: Spectre or APS? Oversample vs Number of Harmonics Harmonic Trimming...(read more)

Guidelines for Maximizing Speed vs Accuracy for Harmonic Balance - Part 1

Tawna — Fri, 07 Oct 2011 19:00:00 GMT

Greetings, I am often asked for guidelines on maximizing speed vs. accuracy for SpectreRF harmonic balance simulations. In a series of 3 blogs, I'll discuss some of the "knobs" that you can tweak, those being: * Which Engine: Spectre or...(read more)

Measuring Fmax for MOS Transistors

Art3 — Thu, 11 Aug 2011 15:00:00 GMT

The following question has come up in comments: "How do I measure F max for an MOS transistor?" The measurement methodology -- testbench, analysis, calculator setup, stimulus, etc.-- does not change whether you are measuring bipolar transistors...(read more)

Guidelines for Setting Pnoise/HBnoise Sidebands to Get Accurate Results

Tawna — Fri, 05 Aug 2011 22:00:00 GMT

I get quite a few questions from designers along the lines of "How do I set the number of pss/hb harmonics and pnoise/hbnoise sidebands in order to get accurate results?" Here are some general guidelines that I follow: The number of sidebands...(read more)

Q&A: TI Wireless Team Describes Advanced Phase-Noise Characterization for RF Oscillators Using SpectreRF

helenet — Wed, 15 Jun 2011 19:00:00 GMT

In this interview, members of the Texas Instrument wireless group talk about the characterization effort initiated and completed last year between Cadence and IBM using TI RF designs as a pilot. The goal between the two teams was to optimize SpectreRF...(read more)

My Favorite nport Settings for Spectre and SpectreRF

Tawna — Wed, 23 Mar 2011 17:00:00 GMT

The nport component located in analogLib can be used in circuits for Spectre and SpectreRF simulations. It is a scattering parameter (S-parameter) based distributed multi-port element. The nport truly is a "black box"… It can be used...(read more)

Tips for Simulating a Transmit Mixer in SpectreRF

Tawna — Thu, 10 Mar 2011 21:00:00 GMT

Some typical questions that I receive from newer SpectreRF users are: How do I simulate a transmit mixer? How do I look at both upper and lower sidebands? How do I set up my simulation for PAC and Pnoise? When I plot my data, how do the indexes correspond...(read more)

Measuring Transistor fmax

Art3 — Tue, 07 Dec 2010 22:00:00 GMT

There were several questions about measuring transistor f max in comments posted to my previous Measuring Transistor f t and Simulating MOS Transistor f t blog posts. So in this posting we will look at simulating transistor s-parameters and device characteristics...(read more)

New Fast Envelope in MMSIM10.1 is Really Fast and Accurate!

Tawna — Tue, 16 Nov 2010 00:00:00 GMT

Traditionally, envelope analysis is used to simulate circuits with modulated inputs. Envelope analysis is much faster than transient simulation, and is used for simulating spectral regrowth. Regular envelope analysis is "brute force" transistor...(read more)

Virtuoso APS Supports RF Analyses in MMSIM 7.2 and MMSIM 10.1

Tawna — Sat, 30 Oct 2010 00:00:00 GMT

A new multi-threading capability has greatly improved simulation speed for RF Designers! In MMSIM7.2, we introduced APS for Harmonic Balance analyses (multi-threaded harmonic balance simulation). In MMSIM10.1, we added support for APS in Shooting PSS...(read more)

Measure Twice, Cut Once for Transistor ft

Art3 — Wed, 06 Oct 2010 16:00:00 GMT

Recently there was an inquiry about the methodology for performing the f t (transition frequency) versus Ic measurement described in my Measuring Transistor f t blog post from July 2008: By bid75 on September 8, 2010 I am unable to understand how ft vs...(read more)

New Time-Saving Feature in IC6.1.4 ISR2: Plot S-Parameter Data Directly From ViVA!

Tawna — Thu, 20 May 2010 17:28:00 GMT

If you haven't heard about it....there is a new feature in IC6.1.4 ISR2 which makes troubleshooting circuits containing nports ( s-parameters ) much easier and faster! Starting i n IC6.1.4 ISR2, you can now plot s-parameters directly in ViVA (without...(read more)

Using RF Simulation Technology for Analog Applications

Hany — Tue, 18 May 2010 22:57:00 GMT

The particular nature of analog circuits puts restrictive requirements on circuit simulators. The EDA industry has introduced proven shortcuts to deliver simulation speed and accuracy for specific applications, e.g. Harmonic Balance for RF and partitioning...(read more)

Using The Composite Triple Beat Source to Speed up QPSS Analysis

Tawna — Thu, 14 Jan 2010 14:00:00 GMT

Say you have a design with 4 input frequencies: 3164M (vco), 1449M (tone0), 1456M (tone1), 1442M (tone2). Currently when you do a qpss analysis, you are inserting a total of 4 separate ports in your schematic and running a simulation. There is a divide...(read more)

NPORT S-Parameter Model Enhancements

Tawna — Wed, 30 Dec 2009 14:00:00 GMT

In MMSIM 7.2, two new parameters have been added to the Spectre nport primitive: datatrunc and causality . In MMSIM 7.1, passivity checking was added. The nport now has causality correction, passivity checking and enforcement, and the ability to remove...(read more)

Analyzing Distortion With Spectre RF

Art3 — Fri, 18 Dec 2009 18:30:00 GMT

Greetings, In the previous appends, we looked at using Shooting Newton Periodic Steady-State analysis to analyze analog circuits. In this append, we will look at using Harmonic Balance Periodic Steady-State, HBPSS, to analyze analog circuits. HBPSS is...(read more)

RF Measurement Library: Capturing Circuit Characterization Setups on the Schematic

alanw — Thu, 16 Jul 2009 13:00:00 GMT

Another design approach that Cadence supports that may not be obvious to all users… The process of setting up a circuit simulation has historically been one of setting up all of the simulation control parameters (i.e. which analysis you want to...(read more)

Periodic Steady-State Analysis for DC-to-DC Converters

Art3 — Tue, 30 Jun 2009 14:30:00 GMT

In " Spectre RF by any other name ...", a non-RF application for Spectre RF's periodic steady-state analysis was introduced. An example of using periodic steady-state analysis [PSS] to simulate the dynamic performance: THD and SFDR, of a...(read more)

Join us at the Cadence booth at the International Microwave Symposium

Hany — Mon, 08 Jun 2009 21:00:00 GMT

If you listened to Tom's advice on this blog two months ago and registered for the International Microwave Symposium or the RFIC symposium, then you should be at the Boston Convention center now enjoying RFIC talks. Please remember that we are waiting...(read more)

Enhanced pnoise Algorithm to Compute Phase-Noise for VCOs with Bandgap Voltage Reference

helenet — Fri, 01 May 2009 13:00:00 GMT

Accurate phase-noise characterization is critical in the design of RF and microwave communication systems. SpectreRF ’s shooting PSS/Pnoise analysis has been the golden simulator for the phase-noise simulation, and close correlation between the...(read more)

2009 RFIC Symposium in Boston - Are You Going?

TomC — Mon, 27 Apr 2009 13:01:00 GMT

If you are an RFIC designer then I hope you are planning on attending the 2009 RFIC Symposium and the International Microwave Symposium (IMS) which will be held in Boston, Massachusetts, as the centerpieces of Microwave Week 2009, scheduled from Sunday...(read more)

Spectre RF By Any Other Name ...

Art3 — Wed, 22 Apr 2009 13:00:00 GMT

It has been a while since I last appende d , hope you are well! It was a little bit difficult to come up with a subject to write about and then recently I was in a meeting where we were talking about transient noise analysis. A designer was discussing...(read more)

Setting VIVA Waveform Color Defaults When Using ADE

dondnile — Tue, 21 Apr 2009 13:00:00 GMT

I found myself getting a little bit frustrated with some of the default colors that would come up in the VIVA waveform tool while I was plotting from the Analog Design Environment (ADE). After working with Kabir, the Product Engineer for VIVA, I discovered...(read more)

Setting Up Harmonic Balance - Part 1

dondnile — Wed, 18 Mar 2009 19:01:00 GMT

This is the first of a series of Blogs to talk about how to fill out the forms for Harmonic Balance. I will include our suggested settings and some helpful hints. I will add to these over time as new things come up both from us and our customer base....(read more)

Shhhhh.....SpectreRF Tutorials and AppNotes - One of Our Best Kept Secrets!

Tawna — Mon, 09 Feb 2009 11:00:00 GMT

Did you know that we have hidden a wide variety of SpectreRF Tutorials, Workshops, and Appnotes in your MMSIM hieararchy? In your <MMSIM71>/tools/spectre/examples/SpectreRF_workshop directory there are the following tutorials, appNotes, and workshops...(read more)

SpectreRF Turbo: Parasitic Reduction

dondnile — Mon, 02 Feb 2009 11:00:00 GMT

I wanted to share some experiences I had with SpectreRF-Turbo and Parasitic reduction on a recent large benchmark. The things I learned may be helpful to anyone who wants to get the most out of turbo and parasitic reduction. Available in MMSIM7.0.1 and...(read more)

Noise and Jitter Analysis for PLL-Based Frequency Synthethiser Using SpectreRF

helenet — Wed, 28 Jan 2009 16:37:00 GMT

Cadence will present SpectreRF Noise aware PLL flow latest enhancements at the DesignCon 2009 conference, based in Santa Clara . In the paper "Noise and Jitter Analysis for PLL-Based Frequency Synthesizer", we fully describe SpectreRF flow and...(read more)

SpectreRF GUI Support for MMSIM 7.1

Tawna — Fri, 23 Jan 2009 14:00:00 GMT

MMSIM 7.1 has just been released! The following IC release GUIs support the new MMSIM7.1 features: IC5.1.41.500.5.129 (However, USR6 or later is strongly recommended) IC6.1.1 ISR65 IC6.1.3 ISR5 And later subversions. For more information, similar tips...(read more)

MMSIM 7.1 Enhancements Benefit RF Designers!

Tawna — Wed, 14 Jan 2009 20:00:00 GMT

The 7.1 release of MMSIM is scheduled for mid-January. There are many exciting RF enhancements that will be useful for RF designers. 1. Three new RF analyses using the harmonic balance engine, have been introduced to make the Spectre RF easier to use...(read more)

Tip of the Week: Guidelines for getting accurate HB QPSS/QPNoise results

Tawna — Fri, 09 Jan 2009 14:00:00 GMT

Two of the most important parameters for accuracy are: (1) maxharms (2) oversample maxharms: The accuracy of HB is greatly dependent on the number of harmonics chosen. As a general rule, you should simulate with with maxharms [5 3] and (if memory allows...(read more)

How to Simulate a Subcircuit (Netlist) With Spectre in ADE

Tawna — Wed, 07 Jan 2009 21:00:00 GMT

Many users ask, "How do I instantiate a netlist into my schematic and simulate with spectre in ADE?" To instantiate a subcircuit (netlist) in your schematic and simulate with spectre in ADE you need to create a cell with a CDF parameter 'model'...(read more)

Going broadside with electromagnetic modeling of advanced processes

TomC — Thu, 09 Oct 2008 13:30:00 GMT

It has caught my attention that designs using fabrication processes such as 65nm, 45nm, 32nm, and smaller, have changed the landscape when it comes to electromagnetic (EM) modeling of components and interconnects. These designs have to contend with the...(read more)

Tip of the Week: When should I use the pss/qpss Harmonic Balance vs. Shooting Newton Engine?

Tawna — Wed, 03 Sep 2008 12:02:00 GMT

Shooting Newton (shooting) and harmonic balance (HB) are complementary technologies and used for circuits that exhibit different behaviors. The shooting Newton algorithm uses an adaptive time step control, which is particularly effective for sharp transitions...(read more)

Tip of the Week: Guidelines for simulating oscillators - phase noise simulations

Tawna — Tue, 26 Aug 2008 15:07:00 GMT

When simulating oscillators, it is important to choose the correct simulator engine (shooting Newton vs. harmonic balance.) In general, we suggest that you use the HB (harmonic balance) engine as your first choice. In addition, there are situations where...(read more)

Tip of the Week: New nport parameter ( dcextrap ) for modeling longer transmission lines

Tawna — Mon, 18 Aug 2008 18:21:00 GMT

There is a new nport parameter, dcextrap, available in MMSIM 6.2.1. The values are constant or unwrap. The default is constant. dcextrap is typically used when the nport s-parameter data file models a system with long delay – and -- the DC point...(read more)

Simulating MOS Transistor ft

Art3 — Sat, 09 Aug 2008 07:25:00 GMT

One other question that you might ask is, this approach works for bipolars but what happens when you need to characterize a MOS transistor. Nothing changes, use the same testbench and measurements, see figure 1. In this testbench a MOS transistor is being...(read more)

Tip Of the Week: analogLib mtline now has a cross sectional viewer when Type of Input=Field Solver

Tawna — Mon, 04 Aug 2008 18:10:00 GMT

Many users have indicated that it is challenging to correctly enter complex transmission lines (multiple conductors, conductors at different heights, and multiple dielectrics) into the analogLib mtline when using the Field Solver Type of Input. You wanted...(read more)

Tip of the Week: Why Do Shooting and Harmonic Balance Phase Noise Results Differ?

Tawna — Tue, 29 Jul 2008 15:12:00 GMT

Question: You are simulating your VCO in SpectreRF. You ran your PSS + Pnoise (noisetype=sources) simulations using the Shooting engine pss+pnoise and plotted the phase noise. You noticed that the SpectreRF phase noise results differ significantly for...(read more)

Tip of the Week: Please explain in more practical (less theoretical) terms the concept of "oscillator line width."

Tawna — Fri, 25 Jul 2008 22:45:00 GMT

Question: From spectre -h pnoise. I find the definition for oscillator linewidth: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ " In a phase noise analysis for an oscillator, the line width, which is also known as the corner frequency...(read more)

Measuring Transistor ft

Art3 — Wed, 16 Jul 2008 13:30:00 GMT

So let’s consider a practical example of creating test benches and performing measurements, starting with how to characterize a transistor. A couple of questions to consider before starting are:

What parameters do you want to measure?
What types of test benches are required to measure these parameters?

Let’s start by considering how to measure the ft of a transistor, ft is a standard figure of merit used by analog designers to evaluate a transistor’s performance. Later we will consider how to measure some other common transistor parameters fmax, Noise Figure, as well as, measuring device stability.

First, let’s review the meaning of ft. It is defined as the unity gain frequency of a transistor’s short circuit current gain. The first point is that we need to measure the short circuit current gain so ideally the output terminal, collector [drain] of the transistor will be connected to a power supply. The next point is that we need to calculate the current gain of the transistor. For Virtuoso Analog Design Environment users, the Virtuoso Visualization and Analysis waveform calculator can be used to perform this measurement. To calculate ft, plot the current gain by dividing the collector [drain] current by the base [gate] current and then using the cross function to find the unity gain frequency. An example of calculating ft, is shown in Figure 1.

Figure 1: Measuring Transistor f_t

When creating a simulation test bench the natural place to start is the actual measurement test bench. To measure ft, an RF network analyzer can be used to measure the s-parameters and then the s-parameters can be converted into h-parameters. By plotting the h21, the ft can be estimated by extrapolating the unity gain frequency of the h21. This approach works well in the lab because wideband shorts do not exist in the real world. So RF measurements need to be performed with input and output matching and a result s-parameters are the natural method for characterizing transistors. One issue when testing in the lab is the need to for separate bias and RF sources. Typically these sources are isolated with a bias T. In place of a bias T, we will use an inductor [pass the bias voltage at dc] and a capacitor [pass the RF input at frequency].

Figure 2: Emulating the Network Analyzer Setup to Measure h21

Using the lab test bench introduces some complexity that is not required when performing the measurement in simulation. By taking advantage of the “ideal” nature simulation, the test bench can be simplified. In simulation, we can create a perfect short using a voltage source. The voltage source provides bias and acts as a short circuit replacing the output matching circuitry in the original test bench. The RF input has been replaced by a current source with ac magnitude of 1 so the current gain can be directly measured. The input bias is still controlled by setting a dc voltage, see
Figure 3. This test bench works well when measuring ft for a single bias condition. However, it is difficult to sweep the bias current of the transistor as can be done in the lab with a bias generator.

Figure 3: Enhanced Test bench with an Output Short

The next enhancement is to replace the bias voltage source and resistor with a diode connected transistor and a current source to set the bias current of the device under test [DUT], see Figure 4. Using a diode connected transistor to generate the bias voltage allows the bias current to be easily controlled. The dc bias and the RF input are still isolated by the pseudo bias T. This change to the test bench allows a designer to characterize the effect of bias current on ft so the transistor can be operated at its maximum ft.

Figure 4: Improved ft Testbench

Another enhancement to the test bench would be to replace the inductor and the capacitor used in the pseudo bias-T, shown in Figure 5. Virtuoso Spectre simulator provides users analysis dependent switches that can be set to open and closed depending on the analysis to be performed. This allows the designer to use the same test bench to perform multiple tests, for example, NF, fmax, etc.

Figure 5: Using analysis dependent switches

The test bench I use to measure ft is even simpler, the the bias network [diode, analysis dependent switches, and RF source] is replaced by an ideal current mirror. The current mirror provides feedback to stabilize the bias point. The current source that sets the bias current is also RF input source the bias T is eliminated. BTW, you might recognize this type of circuit, it is called a Wilson current mirror, shown in Figure 6.

Figure 6: My ft Test bench
To review the test bench development process, we started by replicating the test bench we used in the lab in simulation. Then the test bench was optimized by tuning it to take advantage the “ideal” nature of a SPICE simulator. Along the way we made several improvement to the measurements process.
1) Directly measured the ft, eliminating the need to generate the s-parameters and then calculate the h-parameters.
2) Added the ability to sweep the bias current so plots of ft vs. Ic can be generated, see Figure 7.

Figure 7: Plot of ft vs. Ic

In closing, I hope that this example of creating a test bench and making measurements will be useful for you. Please let me know what you think.

Best Regards,
Art Schaldenbrand

Inductors On Demand, at least one RF design task can be really automated!

Hany — Mon, 14 Jul 2008 02:52:00 GMT

Inductors, transformers and transmission lines are critical components in any high frequency integrated circuit. Conventional electromagnetic tools used for the design of these components are difficult to setup, require electromagnetic expertise and are not integrated in IC design flows.

Traditionally, specialized modeling teams work hard for several months to design, fabricate and characterize a limited set of inductors and transformers for IC designers to choose from. They repeat this long and cumbersome procedure every time a new process node or a new design application is introduced, adding months to the overall design cycle. IC designers faced by a small selection of passive components and limited analysis capabilities are forced to over design wasting expensive Silicon area and increasing failure rates.

Virtuoso Passive Component Designer is a complete flow for the design, analysis and modeling of inductors, transformers and transmission lines. Tightly integrated with Virtuoso Schematic Editor and Virtuoso Layout Suite, the tool brings passive component design to the hands of analog and RF designers.

Starting from design specifications such as inductance, quality factor and frequency, designers can use Virtuoso PCD to automatically generate the optimum inductive device for their specific application and process technology, resulting in higher performance and smaller area. A built-in accurate 3D full wave solver is used to verify the generated devices, eliminating the need for a dedicated inductor characterization run and reducing the design turn-around-time.

Virtuoso PCD is easy to use and does not require electromagnetic expertise. The output is a complete PDK component with a symbol, schematic, layout and a simulation model. The built-in modeling capability converts S-parameter files into physical lumped element models, ready for RF analysis using Virtuoso Spectre Simulator XL and GXL. Virtuoso PCD also includes a fast and accurate coupling analysis capability enabling designers to optimize the placement of inductors and transformers on the layout resulting in smaller Silicon area and higher yield.

Learn more about Virtuoso Passive Component Designer at:

Senrinotabi

Art3 — Sat, 12 Jul 2008 04:54:00 GMT

Greetings! My name is Art Schaldenbrand and I have been at Cadence for 12 years supporting the custom IC design tools in the Virtuoso platform. My interests tend to be as widely varied as the customers I work with, ranging from Wireless Design to CMOS Image Sensor design and Power Management design.

One common theme that comes up when talking to customers about any aspect of design is the challenge of using simulation to understand their design, from creating testbenches to measuring circuit parameters.

In subsequent appends, I would like to discuss these issues and share ideas with you about how to use simulation more effectively.

- Art

Cadence, the new kid on the Electromagnetic Solver Block

Kabir — Fri, 11 Jul 2008 15:57:00 GMT

On June 16 2008, Cadence introduced a new Electromagnetic (EM) solver technology to address the challenges of verifying wireless integrated circuits implemented in advanced CMOS process nodes. You can read the press release here.

How is this going to help the RF designer? Virtuoso® RF Designer brings a fast planar 3D EM solver to the designer's desktop. With its NlogN speed (where N is the number of unknowns), higher capacity, parallel and adaptive frequency sweep, and tighter integration inside the Cadence Virtuoso® environment, Virtuoso RF Designer makes EM simulation an integral part of the RF IC design flow, as opposed to a stand-alone step.

Virtuoso RF Designer integrates seamlessly into the Virtuoso front-end and leverages Cadence's patented electromagnetic analysis technology to accelerate and accommodate large designs found in today's RFICs, PCBs, and SiPs. It's accuracy has been benchmarked over the last several years by comparing with measurement data from TSMC, IBM, Jazz, and other captive foundries.

Questions or comments? Let me know!