With this technique one can add other poles or even zeros if necessary, to accurately simulate the circuit behavior. The second pole is at 17 MHz, where the phase becomes 45 deg. The Bode plot is shown in Figure 4.Īs expected, the first pole is at 24 Hz, where the phase becomes 135 deg (45 deg phase shift versus the phase at low frequencies). If we simulate this model the open loop Bode plot resembles exactly the body plot shown in the ADA4004 datasheet, Rev. Click the figure to expand it.Īnd now comes the test. They are not real components, but they model a mathematical behavior of the real circuit, and this is what we want to accomplish.
#Op amp offset voltage spice model full
In doing so, we take full advantage of the ideal components we use in this model. Why? The VCCSs have high input/output impedance, so each pole impedance at any frequency cannot influence the behavior of the other pole. We can do this, because the two poles are isolated between them. We will insert the second pole circuitry between the capacitor C and the Voltage-Controlled-Voltage-Source (VCVS) at the model output. As we built this model, we arrived at the version shown in Part 2, Figure 4, and it is shown again here, in Figure 2 for convenience. Now, let’s insert this pole in our model. At low frequencies its gain should be 1, so that the overall open-loop gain remains 500000. This second pole influence has to be only at high frequencies. Since the DC open-loop gain is already set by the first pole, we only need to make sure that the choice of current and resistor does not affect the DC gain. The pole can be introduced using the same technique we used in Part 2. The ADA4610-1 is a single amplifier, the ADA4610-2 is a dual amplifier, and the ADA4610-4 is a quad amplifier. Therefore, we need another pole in our model at 17 MHz. The ADA4610-1 /ADA4610-2/ ADA4610-4 are precision junction field effect transistor (JFET) amplifiers that feature low input noise voltage, current noise, offset voltage, input bias current, and rail-to-rail output. Indeed, the phase starts dropping after 1 MHz and becomes 45 degrees at 17 MHz. However, our op amp example, ADA4004 from Analog Devices, shows an extra pole after 1 MHz. In Part 2, we left off at the open-loop bode plot. We talked about modeling the offset voltage, the input resistance and capacitance both common-mode and differential, the output resistance and the frequency domain behavior.
#Op amp offset voltage spice model how to
:Build an Op Amp SPICE Model from Its Datasheet – Part 1 and Part 2 show you how to build an Op Amp SPICE model based on the manufacturer’s datasheet.
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