an1434.pdf (827 KB)
an1725.pdf (1.12 MB)
isl55210.pdf (981 KB)
isla112p50.pdf (1.19 MB)
So now we're gonna show how you actually can demonstrate the level of performance that we're talking about on this ISL55210 plus the ISLA112P50 12-bit 500 megasample daughter board. All of this is available to you from the Intersil website, but let's look in detail at what we're doing to get to this, to demonstrate this performance. First of all, of course we have a signal generator, a bandpass filter, we have our ADC board, we have a clock generator, we have our data capture board, and that is driven from our converter software that is a free download from the Intersil website.
Now of course, when we're testing converters, we're usually looking, with single or two-tone testing to illustrate the capability of narrow-band capability of the converter. So we start out with a very low phase noise signal generator, that we show here. Here we're testing at a single tone, 105 megahertz input frequency. And we're coming out with only a minus four dBm power level. Recall in the interface that we're working with, we are providing quite a bit of gain from board edge. So we only are using a minus four dBm. Now, what's critical about these test sources, for really showing the capability of the amplifier plus the converter, is that they be very low phase noise sources. Not only do we need a low phase noise on the clock, but we need a low phase noise on the source as well.
The next element in our signal data acquisition evaluation system is of course a filter. While our signal sources are very low phase noise, they're extremely poor harmonic distortion. If we don't cut off all those harmonics, we'll see those in our ADC FFT. So what we're doing here is we're taking the output at 105 megahertz into a tunable bandpass filter. This particular one that we use is a 65 to 125 megahertz, with a 5% bandwidth. What we're trying to achieve is a single tone output with a narrow noise bandwidth, so that we can expose the full capability of our amplifier plus ADC performance. One additional element we use is an output attenuator, because the output impedance of these filters is not super well-controlled out of band, so we get a little bit better using this attenuator before we hit the amplifier.
So the next element that we require for a lab environment data acquisition test system is a very good clock. Now, here we're using a Crystek 500 megahertz clock, which has the unique capability of extremely low phase noise. This of course helps us show the SNR capability of the converter. Now that clock is generating a 500 megahertz clock signal that we then bandpass filter before we drive the ADC. Now on the daughter board itself, we have now a good clock coming in, and a good 105 megahertz signal coming in. We have a signal here. We're coming in to a transformer that converts our single-ended signal to a differential signal, where we're running the FDA as a differential IO port. And then on the output side, we've implemented an RLC second-order filter, which also includes a way to tap off our signal for a network analyzer, right at the input to the ADC. So we can actually measure the frequency response up to the converter input in situ.
In a sense we're testing what the frequency response is to the converter, while the converter is operating exactly like it would be in a system. So here we have a transformer, amplifier, filter, 500 megahertz 12-Bit ADC, the ISLA112P50, very low power for 500 megahertz, well under a half watt. And then we have a data capture board, that is available as a motherboard from Intersil. This hosts any one of a series of daughter boards. In this case, we're using the new one with the amplifier. But we also of course offer ones that are just the converter. They all work with the same kind of daughter board, and they're run by a set of software that is the Intersil converter software. So let's turn next to that.