Monday, October 22, 2012

Taking Advantage of Double and Triple Modulation in a Two Channel Waveform Generator

In this post we will look at two modulation capabilities found in some two channel waveform generators that we shall refer to as "Double Modulation" (DM) and "Triple Modulation" (TM). DM and TM give you the ability to create some complex waveforms that are not possible with a single channel generator or, in some cases, with an arbitrary waveform created in external software.

DM is the ability to modulate one of the waveform generator's channels with either the internal modulation engine or an external source and then modulate the other channel with the first modulated channel. That explanation is a little confusing so lets use a diagram to clarify. The below figure shows a high level diagram of how the two channel waveform generators from Agilent's 33500B series performs DM (33510B, 33520B, 33522B, and the 33522A).

High level overview of how DM is done in two channel waveform generators from the 33500B series
The above figure shows how two channel waveform generators from the 33500B series perform DM in their main FPGA. Notice that there are four independent waveform generation engines in the FPGA. Two waveform engines are used for channel 1 and 2. The other two less capable engines serve as an internal modulation sources for channel 1 and 2. In the figure channel 2 can be modulated by an external source or the channel 2 modulation waveform engine. From there channel 1 would be modulated using channel 2 as the modulation source, the resulting double modulated waveform will be outputted from channel 1.

Let's look at two examples that takes advantage of using double modulation. In the first example we want to simulate a non-ideal 10 MHz clock signal by adding both random jitter and deterministic jitter in the form of duty-cycle dependent jitter. For the random jitter we want 75 ps of RMS jitter. For the duty-cycle dependent jitter we want a 10 KHz square wave. To build this non-ideal clock signal with double modulation using a 33522B waveform generator we first set the waveform on channel 2 for a 10 KHz squarewave, this is the deterministic jitter. We then modulate the channel 2 waveform with random noise using sum modulation (mathematically add the noise signal to the squarewave). We then set channel 1 to our 10 MHz clock signal and phase modulate it with channel 2 to add the jitter. To obtain the desired jitter magnitudes it is balance between adjusting the sum modulation magnitude on channel 2 and the phase magnitude adjust on channel 1. The example non-ideal clock signal was generated and the resulting random and deterministic jitter can be seen in the scope capture below. The figure shows a zoomed-in view of the clock signal's rising edge. The histogram's standard deviation represents the random jitter's RMS value which is 75.07 ps (click on figure to enlarge). The outlying edges that are about 1.5 ns from the ideal edge is the deterministic jitter from the 10 KHz squarewave.

10 MHz clock signal with random and deterministic jitter
Note that if we refer back to the first figure of the FPGA, the example non-ideal clock signal is using three of the four waveform generators engines: main engine channel 1, main engine channel 2, and modulation engine channel 2.

Let's look at another example where we create a four tone signal and use all four waveform engines to achieve TM. Our four tone signal will consist of tone frequencies 15 MHz, 20 MHz, 25 MHz, and 30 MHz. To build the four tone signal we set channel 1 to a 20 MHz sinewave and sum modulate it with a 15 MHz sinewave. For channel 2 the same steps were repeated except 30 MHz and 25 MHz frequencies were used. The Channel Combine feature on the 33522B was used to mathematically add channel 2 to channel 1. The resulting four tone signal can be seen in the figure below.

Note that the TM abilities in a 2 channel waveform generator are not as capable as the DM capabilities since the channels can only be combined or summed together. This can be used for creating a four tone signal like we just saw or for summing an I and Q signal together.

In this blog post we looked at how a two channel waveform can be used to do double modulation and even triple modulation. If you have any personal insights to add to this post use the comments section below. If you have any questions from the post feel free to email me.

Click here for more info on the 33500B family of waveform generators


  1. افضل شركة تنظيف خزانات بالاحساء و بالدمام

    تنظيف الخزانات من الامور الهامة فشركة الاول شركة تنظيف خزانات بالاحساء لديها افضل خدمات تنظيف خزانات بالدمام من التطهير والتعقيم والتنظيف على اكمل وجة فشركة الاول لخدمات تنظيف خزانات بالاحساء لديها امكانيه التنظيف وغسيل جميع انواع الحزانات من خزان العلوى والارضى والخرسانيه بطريقة احترافية تساعد على ازالة كل الترسوبات والمتواجدة فى الخزان والاهتمام باعمال التعقيم من خلال افضل مواد متواجدة ومتعارف عليها ذات جودة عالمية دون ان ثؤثر على مياه الشرب فالاول افضل شركة تنظيف خزانات بالدمام و تتميز باسعارها التى تناسب الجميع وانظباط المواعيد وتتميز بعمالة مدربة على جميع انواع الخزانات


    افضل شركة تنظيف خزانات بالرياض

    تنظيف الخزانات من الامور الهامة فشركة الاول شركة تنظيف خزانات بالرياض لديها افضل خدمات الخاصة بعمليات تنظيف خزانات بالرياض من التطهير والتعقيم والتنظيف على اكمل وجة فشركة الاول لتنظيف خزانات لديها امكانيه التنظيف و غسيل خزانات بالرياض
    جميع انواع الحزانات من خزان العلوى والارضى والخرسانيه بطريقة احترافية تساعد على ازالة كل الترسوبات والمتواجدة فى الخزان والاهتمام باعمال التعقيم من خلال افضل مواد متواجدة ومتعارف عليها ذات جودة عالمية دون ان ثؤثر على مياه الشرب

  2. أفضل مستوي في خدمات تسليك المجاري يمكنكم الآن الحصول عليها من خلال فريق شركة تسليك مجارى بالدمام و هي شركة أبراج دبي المتخصصة و التي تقدم أعلي مستوي خدمات و بأوفر الأسعار .

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