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How's it going? My name is Noel Melberger from the Medical Systems Engineering and Marketing team at Texas Instruments. Today, I'll be going over a simulation created to showcase TI solutions for subcircuits within the electrosurgery generator and equipment using PSpice for TI as the simulation platform.

In today's discussion, I'll be going over a few of the subcircuits, including the RF amplification stage and pieces of the high-speed signal path. So just as a quick overview of how the signal and electrosurgery generators moves within the system, a signal is generated in either a DSP or FPGA. It's a digital signal.

That digital signal, it then goes through a DAC to turn it into an analog signal. That signal is fed to the RF amplification stage to be amplified. And that amplified signal is then used in the active electrode to actually cut and coagulate tissue on the patient.

So this signal generally is a high-power, high-frequency RF signal. In the case of this simulation, we're working with a 500 kilohertz sine wave. It's starting off as a 0.5 volt plus/minus or a 1 volt peak-to-peak 500 kilohertz sine wave at the input of the RF amplifier, is then amplified to be 200 volts peak-to-peak, still 500 kilohertz.

So today, we'll be looking at the RF amplifier, the current and voltage sensing of the RF amplifier output, along with the translation from the deck to be used with the RF amplifier. So before we get into any of these pieces, let's take a quick look at what sources we're using for this design.

For starters, we have a plus/minus 10-volt rails that are used for the operational amplifier in the RF amplification stage. We also have a 200-volt rail that is used for the push-pull amplifier part of the RF amplifier stage.

In addition, we have plus/minus 5 volt rails, which are used for the amplifier in the current and voltage sensing phase. In addition to that, we also have a source that is being used to simulate the output current of the RF amplifier.

That way, we can show the functionality of the current sensing portion of the design. And we also have two sources that are used to simulate the differential output of our DAC 904, which is the DAC chosen for this design.

So let's first look at the translation from the DAC 904 to a signal that can be used with the RF amplifier. So the DAC 904 is a 125 mega sample per second DAC that outputs a differential current output with a maximum of 20 milliamps peak-to-peak.

So essentially, what this circuit is doing is it's taking that differential current output from the DAC and translating it to a single-ended voltage input for the RF amplifier.

For this design, we're using the THS4061. This is a 180-megahertz high-output drive voltage feedback amplifier. And essentially, what we're getting on the output is a 1 volt peak-to-peak 500 kilohertz sine wave.

So let's take a look at the output and make sure it matches our expectations. Here, I'm putting a voltage probe on the output and running a transient simulation to see what the output looks like. And we'll just give this a second to load.

So here, as you can see, as we expected, we're getting a 1 volt peak-to-peak or plus/minus 0.5 volt, 500 kilohertz sine wave, which is what we'll be inputting to the RF amplifier stage of the design. So now, let's take a look at that RF amplifier.

Here, you'll see we have a push-pull configuration being driven by our THS4051. The THS4051 is a 70-megahertz op amp with a [INAUDIBLE] rate of 240 volts per microsecond, making it a great fit for driving a push-pull amplifier such as this at high frequencies, which we're using, in this case 500 kilohertz.

So that RF amp input, which is the output of the DAC translation stage, is coming in here, and we're gaining it up to 200 volts peak-to-peak on the output. We're also using a transformer to bump up the voltage as well. This happens to be a 2-to-1 turns ratio transformer, effectively allowing us to double the output voltage. We're also using a 50-ohm resistor to simulate a max current of 2 amps on the output.

So another reason why this transformer is important is to add an isolation between the patient side of the design from the rest of the circuitry, which is essential for safety aspects of many medical designs, including electrosurgery generators.

So if we take a look at the output of this RF amplifier, what we expect is a 200 volt peak-to-peak sine wave at 500 kilohertz, ideally with as little distortion as possible. As you can see, that's what we're getting.

Relatively low distortion, and the distortion can actually be decreased further by changing the load resistance and having a slightly lower current output. So this signal right here is actually what is being sent to the active electrode to cause the cutting and coagulation of tissue.

Next, let's take a look at the current and voltage sensing stage. So this is used to sense the voltage and current on the output of the RF amplifier. It essentially tells us the voltage and current that is going into the patient.

Here, we're using two THS4130s. This is a high-speed, low-noise current feedback amplifier that's capable of 150-megahertz bandwidth. What makes these op amps a really perfect fit for this application is the low input referred noise of only 1.3 nanovolts per square root hertz, along with its wide power supply range capable of plus/minus 15-volt dual supply.

The output of these amplifiers have a glitch filter, which effectively allows it to minimize the amount of noise going into an ADC. These glitch filters are designed to work with our ADC3664, which is a 14-bit, 125 megasample per second, very low noise, dual-channel ADC. What makes this ADC a great fit here is its very low noise of 77.5 dB full scale SNR and it's extremely low latency of two clock cycles.

Again, you'll see that we have some transformers on the output of these amplifiers. And these, again, are used to give some isolation between the patient side and the rest of the design. So now let's take some differential voltage probes and take a look at the outputs of the current and voltage-sensing stage.

Here, what we'd like to see is a 4 volt peak-to-peak output for both the voltage and current. That would be the maximum output, which is designed to fit the scale of the ADC3664.

As you can see, we still have that RF amplifier up here, which is making it a little bit harder to see. So let me remove that. And now you can see what we're getting are the voltage and current sensing outputs, which are indeed 4 volts peak-to-peak, and you can still see that this is a 500-kilohertz signal.

So that is essentially what we have here in this simulation. We're showing the RF amplification stage along with the current and voltage sensing stage, which makes up part of the high-speed signal path that voltage and current sensing signals are sent to an ADC.

And that ADC sends them to an FPGA or DSP in order to do further processing of that signal to create that feedback loop. And that process signal is then taken to the DAC, which feeds it to the RF amplifier, creating a closed-loop system.