Second order systems appear frequently in the design of analog systems as well as digital systems. In most cases these types of systems are difficult to understand analytically and designers must resort to simulations and empirical assessments.
Examples of these types of systems ( or circuits) are PLLs, switching power supplies, analog equalizers, mechanical servomechanisms, filters etc. There are some expressions available to do approximate analysis and design before resorting to long simulations or empirical data gathering. These are mainly based on the second order characteristic equation. Solution of this equation yields at least two very useful quantities. The natural damped frequency and the damping ratio. Use of these parameters can greatly facilitate the analysis and design of second order systems. For a brief cookbook style treatment of this analysis please read the article in our website www.signalpro.biz under engineering pages.
Monday, November 1, 2010
Sunday, October 24, 2010
Cable modeling for high speed data communications
I have not been blogging for a while. The reasons are many, but mostly because of some interesting work that came up. This post is a result of grappling with cable modeling and cable parameter information extraction. The simple comment is, that this is a very tedious affair as very little data is available in the literature. High speed data communication cables come in various disguises. Some of the more popular types are the CATX types and STP ( shielded twisted pair) types. Various gauges are being used. We looked at 24 and 26 AWG types.
The issue is, that if you are designing a cable equalizer for example, you need a cable model. There are a number of ways to do this. The most expensive way is to either buy or rent a laboratory piece of equipment which can perform up to at least 12 Ghz, buy or make connectors, and then make measurements. The other way is to use information available in the literature to build a cable model. The latter is very sparse and difficult to obtain. Anyway both approaches should be tried.
The modeling parameter W in some SPICE based programs is a useful one and with proper manipulation can yield fairly accurate models. It is quite complicated to understand. Simple transmission line models in PSPICE can be used but will only offer very basic models and may not be accurate for design.
There are also cable model ( analytical) parameters available in some text books for coaxial, parallel wire cables, microstrip etc. which can also be used. These can be used to obtain the so-called RLGC SPICE model. Using the RLGC circuit is not enough to model transient response since the cable delay cannot be modeled. A transmission line model is required for this. These too are only first order estimates.
So what is required is more empirical data of cables and cable models. One or two researchers have actually done this. However, the need to model parameters such as attenuation, crosstalk, ISI etc is still an open field, ready for someone to step in and do the needful!
The issue is, that if you are designing a cable equalizer for example, you need a cable model. There are a number of ways to do this. The most expensive way is to either buy or rent a laboratory piece of equipment which can perform up to at least 12 Ghz, buy or make connectors, and then make measurements. The other way is to use information available in the literature to build a cable model. The latter is very sparse and difficult to obtain. Anyway both approaches should be tried.
The modeling parameter W in some SPICE based programs is a useful one and with proper manipulation can yield fairly accurate models. It is quite complicated to understand. Simple transmission line models in PSPICE can be used but will only offer very basic models and may not be accurate for design.
There are also cable model ( analytical) parameters available in some text books for coaxial, parallel wire cables, microstrip etc. which can also be used. These can be used to obtain the so-called RLGC SPICE model. Using the RLGC circuit is not enough to model transient response since the cable delay cannot be modeled. A transmission line model is required for this. These too are only first order estimates.
So what is required is more empirical data of cables and cable models. One or two researchers have actually done this. However, the need to model parameters such as attenuation, crosstalk, ISI etc is still an open field, ready for someone to step in and do the needful!
Saturday, June 26, 2010
High speed digital data communications demand
It appears to the author, that the high speed data communications sector of the market is growing fast. At least this is the conclusion that we must draw from the demands on our design resources from various customers.
USB3, 10G, HDMI, etc are all very demanding in terms of the semiconductor processes to be used ( cost effectively ), design techniques, systems engineering, CAD tools, availability of parameterics of cables, connectors, PCB based information and ultimately design techniques to stitch all of these together into a device or subsystem that will actually work in the real world.
As we work through these designs, we find that there is a vast gap between theory and reality. This includes simulations also. This has always been true in some degree with other technologies but in the case of these designs it becomes critical. Designing the devices to operate robustly in the real world is very time consuming and in many ways an art, rather than a science. Design experience is called for more than anything to implement these techniques from an intuitive point of view. We believe this is going to be a most interesting and challenging series of designs. More as the work proceeds.
USB3, 10G, HDMI, etc are all very demanding in terms of the semiconductor processes to be used ( cost effectively ), design techniques, systems engineering, CAD tools, availability of parameterics of cables, connectors, PCB based information and ultimately design techniques to stitch all of these together into a device or subsystem that will actually work in the real world.
As we work through these designs, we find that there is a vast gap between theory and reality. This includes simulations also. This has always been true in some degree with other technologies but in the case of these designs it becomes critical. Designing the devices to operate robustly in the real world is very time consuming and in many ways an art, rather than a science. Design experience is called for more than anything to implement these techniques from an intuitive point of view. We believe this is going to be a most interesting and challenging series of designs. More as the work proceeds.
A low power crystal oscillator at 32,768 Hz
The frequency 32, 768 Hz, is one of the most popular frequencies for crystal oscillators as it is used in most time keeping applications. With the proper interface circuit ( PLLs ) it can also be used for high frequency synthesizers. The actual quartz is also relatively inexpensive and this lends itself to cost effective frequency circuits and timekeeping. Of course temperature control can aso be used to generate TCXOs.
In any case, we recently designed, fabricated and throroughly analyzed a low power crystal oscillator ( in conjunction with our sister company). The circuit was first pass functional. The crystal oscillator section dissipates a mere 200 - 500 nA of current at the rated frequency.
The entire chip consists of a crystal oscillator, a low power analog buffer, a level converter and a digital output buffer capable of driving 100 pF. In addition the device has a means of trimming the frequency using an analog trim as well as a digital fine trim.
The device was evaluated thoroughly and its temperature characteristics measured extensively. Interested parties may contact us through our website at www.signalpro.biz for our experience and these results. All in all a most satisfying experience!
In any case, we recently designed, fabricated and throroughly analyzed a low power crystal oscillator ( in conjunction with our sister company). The circuit was first pass functional. The crystal oscillator section dissipates a mere 200 - 500 nA of current at the rated frequency.
The entire chip consists of a crystal oscillator, a low power analog buffer, a level converter and a digital output buffer capable of driving 100 pF. In addition the device has a means of trimming the frequency using an analog trim as well as a digital fine trim.
The device was evaluated thoroughly and its temperature characteristics measured extensively. Interested parties may contact us through our website at www.signalpro.biz for our experience and these results. All in all a most satisfying experience!
A new silicon proven Rf device - a first pass success!
A first pass success is always welcome. When the sucess is a high frequency device it is doubly so. The latest addition to the high frequency, silicon proven ASSP portfolio, is a high frequency, wideband amplifer fabricated in a 0.35um SiGe process.
It is fairly general purpose and can be used as gain block, an LNA etc. The basic features are as follows:
Features:
Usable frequency gain = 100 to > 2500 Mhz
19 dB typical ac gain at 900 Mhz, VCC = 2.7V
NFMIN = 1.2 dB at 900 Mhz
NFMIN = 1.5 dB at 2500 Mhz
1 dB compression point at 900 Mz = 2.9 dBm
1 dB compression point at 2500 Mz = 0.9 dBm
OIP3 at 1.5 Ghz = 15.0 dBm
OIP3 at 2.5 Ghz = 10.0 dBm
Power supply from 2.7 to 5.0 Volt
Power supply current typical = 4.7 mA
Reverse isolation s12 = -48.0 dB min.
The device was tested from -55 Degrees C to 125 Degrees C. An extended frequency test was also done at 5.0 Ghz. The gain dropped to 17 dB. Other parameters were also slightly affected.
Anyone with interest in this device and its development may contact the author via the website located at www.signalpro.biz.
It is fairly general purpose and can be used as gain block, an LNA etc. The basic features are as follows:
Features:
Usable frequency gain = 100 to > 2500 Mhz
19 dB typical ac gain at 900 Mhz, VCC = 2.7V
NFMIN = 1.2 dB at 900 Mhz
NFMIN = 1.5 dB at 2500 Mhz
1 dB compression point at 900 Mz = 2.9 dBm
1 dB compression point at 2500 Mz = 0.9 dBm
OIP3 at 1.5 Ghz = 15.0 dBm
OIP3 at 2.5 Ghz = 10.0 dBm
Power supply from 2.7 to 5.0 Volt
Power supply current typical = 4.7 mA
Reverse isolation s12 = -48.0 dB min.
The device was tested from -55 Degrees C to 125 Degrees C. An extended frequency test was also done at 5.0 Ghz. The gain dropped to 17 dB. Other parameters were also slightly affected.
Anyone with interest in this device and its development may contact the author via the website located at www.signalpro.biz.
Monday, May 31, 2010
Change of menu item "Engineering pages"
The menu item in the website ( www.signalpro.biz) has been changed from "Engineering Pages" to " Engineer's corner".
More on the inverted F antenna analysis
An analysis of the printed inverted F antenna was carried out using the NEC2 program. This program is available in the public domain. It models antennas as wires.
One can set the wire radius. The disadvantage of the program is its inability to model dielectrics as substrates. However, in spite of this, with a bit of smarts a lot of information about antennas can be obtained from it. In case of a printed strip, Balanis's book provides the conversion between the wire radius and the width of the strip for those who may be interested in further analysis. Our experience has been that no matter how much modeling is done ( as we did follow up with ADS MOMENTUM)in the end the antenna ends up being tuned by somewhat of a trial and error method. In our opinion both procedures are important. We need a quick way to assess the antenna operation using a program like NEC2 which is surprising fast and a more refined means of simulation like ADS or FEKO. Check out the article in the SPG website ( http://www.signalpro.biz) under engineer's corner for printed antennas. ( Note: "Engineering pages"
has now been changed to "Engineer's corner".
One can set the wire radius. The disadvantage of the program is its inability to model dielectrics as substrates. However, in spite of this, with a bit of smarts a lot of information about antennas can be obtained from it. In case of a printed strip, Balanis's book provides the conversion between the wire radius and the width of the strip for those who may be interested in further analysis. Our experience has been that no matter how much modeling is done ( as we did follow up with ADS MOMENTUM)in the end the antenna ends up being tuned by somewhat of a trial and error method. In our opinion both procedures are important. We need a quick way to assess the antenna operation using a program like NEC2 which is surprising fast and a more refined means of simulation like ADS or FEKO. Check out the article in the SPG website ( http://www.signalpro.biz) under engineer's corner for printed antennas. ( Note: "Engineering pages"
has now been changed to "Engineer's corner".
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