Sunday, December 28, 2008

Viewing Signals: How Rigol Products Raise the Bar

Viewing signals is the 1st order value of an Oscilloscope.

The vast majority of oscilloscope users are primarily concerned with how the product displays signals. RIGOL Technologies has invested engineering and materials in a way to provide the best viewing scopes in their respective class of products.

Our view of oscilloscope especially those that cost < $2000 USD are that viewing is critical and comprises 3 aspects in order to create a superior scope for troubleshooting and basic waveform observation. These three are:

  1. Acquisition – You must have enough performance to accurately capture the signal. The acquisition is often looked at in terms of Bandwidth and sample rate.
    1. RIGOL has designed a variety of front end signal conditioning circuits optimized for different bandwidths. Out highest bandwidth today is 300 MHz which is the highest bandwidth performance in products under $2000 USD.
    2. Sample rate is sometimes confused based on different manufacturer’s current capabilities. So what are the facts?
      1. If you acquiring a signal only once i.e. single shot, you must have more than 2 times the sample rate as the bandwidth. This is according to Nyquist theorem and implies many perfect conditions not possible in the real world, thus you need > 2 times the higher bandwidth.
      2. Certain manufacturers would want you to believe you need 10 times the sample rate of the bandwidth of the scope. While this may be a nice thing to have, it is based more on a manufacturer’s current technology than any real need to accurately acquiring and displaying the signal under test.
      3. In reality, the correct answer is that sample rate should be between 3 and 5 times the bandwidth of the scope. Most scopes today employ a Sinx/x filter in lower end scopes and can do a good job of recreating the signal with 3 to 5 times higher sample rate than the bandwidth of the scope.
      4. Our scopes have been optimized for this performance allowing our customers to not spend too much for digitizing that will bring little incremental advantage.
  2. Isolating Events – In general the real power of a digital scope is to isolate events and store them providing incredible power in troubleshooting. The cornerstone of isolating events is triggering. RIGOL Oscilloscopes have been designed from our inception to provide powerful and easy to use trigger options to make isolating events a breeze.
    1. Trigger modes –
      1. Edge – The traditional trigger of triggering on a rising or falling edge at a certain voltage.
      2. Pulse triggering – Allows the trigger to be set to a pulse either positive or negative and when present for greater than or less than a time that is user defined. This can accomplish tasks like Glitch triggering.
      3. Slope Triggering – Triggering when the slope of a signal transition is faster or slower than the user defined setting. Very useful in looking at tri state conditions.
      4. Pattern Triggering – When using a RIGOL Mixed Signal Oscilloscope (MSO) you can trigger on a pattern of 1, 0 and don’t cars across up to 16 channels.
      5. Alternate – We also provide a alternate trigger when the scope trigger on channel one and acquires channel one, then triggers on channel 2 and displays channel 2, this provides for a true dual time base where each channel can sample at different rates based on there set up.
    2. All told we believe the triggering of the DS 1000 oscilloscope family is the most powerful in this range of products by any manufacturer.
  3. Display – Display is the final part of a great viewing tool. We believe there are three critical areas of display:
    1. The display itself, we have chosen to use TFT color displays in all our products as they provide superior color, brightness and viewing angle to the standard and cheaper LCD display used by most manufacturers today.
    2. Update rate – The speed with which an acquisition can occur provides the real time and responsive feel most customers desire in a scope. RIGOL invests in optimizing the update rate. Our DS 1000C and DS 100CD achieve ~ 1000 waveforms per second and is our newest DS 1000CA we placed an additional FPGA in the scope to increase this to ~2000 waveforms per seconds that we believe is the fastest update rate in this class of oscilloscopes.

The bottom line is that we are RIGOL take viewing signals serious and have invested engineering to provide what we feel is the best viewing scope in its class.

posted by Rigol @ 11:35 AM