ISL55210

This video demonstrates other ways of doing the signal to differential using an FDA with the ISL55210 Active Balun Evaluation Platform.

Transcript

Hello, this is Michael Steffes, the Senior Applications Manager for Renesas' high-speed signal path products. And today we're going to continue our discussion on how to get single to differential conversion in a couple different techniques for your circuits.

Showing on the screen behind me is a very capable technique of using an input balun and a fully-differential amplifier, which has been a very useful technique over the past decade. We're going to move forward from this, of course, to show an active balun approach using the ISL55210. But it's this circuit that you would get on the ISL55210 evaluation board available from Renesas' website or your favorite distributor.

This circuit comes with an input transformer and then an output transformer, really just for measurement purposes. On the input side, we use a range of transformers or baluns to get from single to differential into a termination impedance being set here by the gain resistors. So this is a very nice circuit and it certainly works very well as a low-power, single differential circuit. Once we're balanced on the opposite side, this circuit does have some advantages in terms of second harmonic suppression.

Now, if we move on to this new technique enabled by the ISL55210, we eliminate both the balun, and in this case, we eliminate the resistor to ground that you'll see in everybody else's fully-differential amplifier datasheets or application notes. And we're going to try to do our input match and gain setting just with the resistors we have available in the circuit. If we do that and run a sweep of gains, we can step the gain up from 14dB to 34dB, and see what happens to the resistor values.

One of the really surprising things for instance, at a gain of 20, let's just look at these values, is the input resistor that we end up driving is an extremely low value, 4.57ohm. But the circuit will appear as if it's giving you a 50ohm input match through very broad frequencies. A couple things come out of that, what we're seeing here is that the input match is largely being set by the action of the common-mode loop because that's what's giving us our active termination characteristic. And to hold that match through extremely high frequencies implies you need a very broadband common-mode loop which is one of the unique characteristics of the ISL55210 is it has a common-mode loop band with an exceeding 1.5GHz, whereas, all other FDAs today have a much lower bandwidth on the common-mode loop.

As we look at these extremely low resistor values, we would expect the noise, or the input-referred noise figure, to step down considerably using these 4.5ohm kind of input resistors in the active balun circuit. You can go to another video to see those test results.

This video discusses the ISL55210 Active Balun Evaluation Platform's test results for frequency response and measured noise.

Transcript

Hello, this is Michael Steffes, Senior Applications Manager for High-Speed Signal Path at Renesas. Today we'll continue our discussion on this active balun approach of using a wide band for differential amplifier, the ISL55210.

And so what we are going to do now is we are going to look at detail at the frequency response and the measured noise figure for a couple of configurations of this very flexible approach to getting a input impedence match with broadband single to differential gain with no actual magnetics in the circuit.

So what we show on the screen here is the configuration of the circuit as the board would be delivered of our active balun evaluation board, would be delivered in this configuration on the screen. We actually have three different output interface options. Here we are showing a transmission line balun, which actually gives quite a bit broader frequency response flatness then a more typical flux couple balun but that option is also available on the board.

So if we look at this circuit, we configured it for a 50ohm input match. We've got a 16.4dB gain to the output pans. And we're going to take a 6dB loss in the matching and we are estimating about a .2dB to .4dB insertion loss in the balun. Now that’s not modeled here but we will see it on the measurement of the board.

So let’s run the simulation and we will measure the output all the way through to the final 50ohm load. We should see a response shape that looks something like this. It does simulate at about 10.4dB. Let’s look closely at where we would see about a .5dB roll off from 10.4. So that is going to be 9.9. We should expect to see a .5dB flatness with the higher frequencies, up through about 470MHz is what the simulations would predict. So this is what we would expect to see.

Let’s go over to the network analyzer and see what we really get. We've got our evaluation board configured to measure the response shape. The marker is currently at 10MHz and we see about a 10.2dB measured gain to the max load. And let’s go up in frequency and just see where we start to see a deviation and that is going to happen at about 470MHz, very much like our simulations.

Extremely capable circuit. Let’s go back now and look at our noise performance for this type of circuit. We will go to a little higher gain to check the noise. And if we do that we will use this table and we will see that we need about a 4.60ohm input resister to get a 50ohm match. We'll need about a 543ohm feedback resister on each side. And we should be getting about 450MHz bandwidth in that configuration. So if we configure that active balun board and with those resister values, we can go make a measurement of the input noise figure for a couple different configurations. This green curve we are showing on this comparison plot was actually in the standard configuration with a resister to ground, 110ohm that typically you would see in these kind of circuits. And we can see, it gives about a 10dB noise figure when you get up above the 50MHz region.

If we now do the same input impedance and the same gain setting, but eliminate the resister ground. Completely depending on the current mode loop band to get our match. We'll see the noise figure indeed drop significantly. Down into the 7dB noise figure region. That correlates to approximately a .9nV input preferred noise. And since the ISL55210 has already a .85nV device, this essentially shows that the resister noise contribution using this active balun approach are extremely low. We've essentially taken the resister noise out of the performance of the circuit.

If you like to try these circuits for yourself and measure these noise in different configurations, go on the Renesas website and order the active balun evaluation board, where there is also an application note describing the board.

The demo concludes for the ISL55210 Active Balun Evaluation Platform and discusses input impedance match.

Transcript

Hello, this is Michael Steffes, Senior Applications Manager for high-speed signal path products at Renesas. And we're gonna conclude our series on the active balun approach of using the ISL55210 to get a very broadband single to differential conversion. We've already seen that it gives an extremely flat frequency response through 500MHz. But does it really give a good input impedance match, as the equations would predict?

Turning to a very venerable piece of equipment, the HP or Agilent 4195, we've configured this box with one of our active balun boards to measure the input impedance here. So we've done a calibration from 1MHz to 500MHz, in an S1 one calibration, to measure the input impedance. If we look over that span, the board is powered, and we are taking a measurement, we can trigger it, and we can see that it will update the curves just slightly.

At 10MHz, we're seeing 51ohm, and a minus two degrees, almost perfect match at 10MHz, but continuing and moving out markers up to 500MHz, we'll see that we only deviate up to 53ohm approximately, at 500MHz, and 3.3 degrees. Looking at the magnitudes here, that's better than 30dB return loss over the range of probably about 2MHz to 500MHz. That's a range of input match, just really not supported by any balance. But particularly if you consider we're giving about a 10dB gain to the match load here, which is equivalent to having a turns ratio of about 3.3.

So let's turn back to some of the other characteristics of this circuit, we're obviously are getting a very good input match. So we're trying to emulate a doubly terminated 50ohm environment for output intercept measurement purposes, and that's the purpose of this circuit.

The next step in our intercept measurement, was to come up with an extremely low distortion input signal which we're getting with this pair of power amplifiers, which isolate our signal sources during the measurement process. The test signal coming out here would have the two test tones on them, and we're presenting probably better than a 120dB dynamic range of the source signals, using this approach.

Let's look at our measured data. This is measured using the active balun circuits, set up for a gain of 10dB net to the match load, and a 50ohm input match, that we've discussed previously. Here we’ve got some measured data, and then a fit line, since what we're seeing here is the open loop gain roll off of the ISL55210, up through frequency.

At 200MHz, we're measuring approximately 40dBm to the match load, in a standard output intercept kind of definition. And at 300MHz, we're still above 30dBm. So for a 115mW type device, this is actually exceptional intercept through very high frequencies. The approach certainly works as an IF Amplifier, what else would we use that for?

We could potentially use this in a number of areas, wherever you need a good input match, and of course, it's extremely flexible. If for instance, you need to terminate a cable, and the cable itself is not exactly 50ohm, you can go just go into the equations and put in what you're trying to terminate to, and adjust the resister value to get exact match. So for instance, if you have a cable that needs to be matched, and the cable is not exactly 50ohm, it's 53ohm perhaps, or 55ohm, you can adjust the input resistors to get perfect match over a huge range here.

75ohm systems can be easily be implemented, obviously for cable modem kind of applications. It’s just a very flexible circuit, and wide range of applications.

So go to the Renesas website and order the active balun implementation of the ISL55210, see how you can use it and let us know.

The high-speed ADC evaluation platform enables rapid testing and performance validation of the entire portfolio of low-power 8 to 16-bit, 40 to 500MSPS high-performance analog-to-digital converters.

Resources

• ISL55210
• HS-ADC-EVALKITS

This video demonstrates the platform daughter board that includes both an ISL55210 FDA and an ISLA112P50 12-bit, 500 MSPS ADC.

Resources

• Ultra-Low Power Broadband 8- to 14-Bit Data Acquisition Kit
• ISL55210

This video walks you through the proper set up of your own data acquisition test environment, from the initial signal generator all the way through the data acquisition motherboard. You'll need the daughterboard with the ISL55210 FDA as well as the ISLA112P50 12-bit, 500 MSPS ADC.

Resources

• ISL55210 
• ISLA112P50 12-bit 500 mega-sample daughter board

This video demonstrates the industry-leading performance you can expect with the ISL55210 FDA and ISLA112P50 ADC, and shows you how to use the proprietary data acquisition evaluation software.

Resources

• Ultra-Low Power Broadband 8- to 14-Bit Data Acquisition Kit