# What is the upper and lower frequency limit of the AWG400 series+ AWG500 series+ AWG610 and AWG710?

### 问题：

What is the upper and lower frequency limit of the AWG400 series+ AWG500 series+ AWG610 and AWG710?

### 答案：

Defining an upper frequency limit, is somewhat difficult to do, the limit is dependent on the quality of the waveform needed. There is a hard upper limit of the Nyquist frequency, which is the maximum clock rate divided by 2. However this is not a very practical limit for a lot of applications. For example, the signal-to-noise ratio of a 2 or 3 point per cycle waveform can be poor. Another factor is the waveforms may be beyond the -3 dB point of the output amplifier’s bandwidth, so the output amplitude will be reduced. Generally the practical upper limit that will work for most applications is 4 or more points per cycle, or the maximum clock rate divided by 4. With some applications, waveforms of 2 to 4 points per cycle work just fine, but only the user can determine what upper limit is appropriate for that application.

Another factor that limits the upper frequency is output amplifier bandwidth, and a good way to see the impact is on a square wave. A ideal square wave consists of the fundamental frequency and an infinite number of odd harmonics that roll off in amplitude at a specific rate. If you have a 100 MHz square wave on an AWG510, the 100 MHz seems well within the 250 MHz bandwidth of the output amplifier. However, the first harmonic contained in the waveform is at 300 MHz, the next at 500 MHz, the next at 700 MHz and on out. These harmonics end up being filtered out of the waveform by the amplifier bandwidth limit. The result is that your square wave looks more and more like a sine wave as you increase the frequency.

A different way to look at the impact of bandwidth limiting on a square wave is rise time. Take, for example, a square wave with 8 points per cycle (4 points high and 4 points low) running with a 1 GHz clock on the AWG510. This creates a 125 MHz square wave with a period of 8 ns. An ideal square wave makes instant transition between the low level and high level and then back to low. It would be a perfect square wave if you had an infinitely fast system to translate that data into a waveform. However, in an AWG510 the rise/fall time is 2.5 ns at > 1V p-p. This means that 5 ns (2.5 ns rise and 2.5 ns fall) of the 8 ns period will be spent between the 10% and 90% points of the waveform, or over 60% of the time the waveform transitions from low to high and back again. While this would look somewhat like a square wave, being flat on the peaks, it is starting to look a like more like a sinewave due to the large percentage of time spent in the transitions.

The lower limit is easier to calculate. You take the lowest available clock rate and divide it by the maximum record length. This method assumes that you create a waveform that is 1 cycle over the maximum record length.

Below are the lower limit and the Practical and Nyquist upper limits for the AWG400 series, AWG500 series, AWG610, AWG615, AWG710 and AWG710B:

 Model Max clk. Output risetime / B.W. (D. O. = Direct Out Mode) Min. Freq. Practical / Nyquist AWG410 AWG420 AWG430 200 MHz <4 ns / 87 [email protected]>1 V 617.28 uHz (10 KHz / 16,200,000 points Opt. 01) 50 MHz / 100 MHz AWG510 AWG520 1 GHz <2.5 ns / 140 [email protected]>1 V <1.5 ns / 260 [email protected]