RF Electronics Chapter 10: Operational Amplifiers Page 349
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 10.10. Measured and simulated frequency response of circuit of figure 10.4.
Figure 10.11 shows the final prototype hardware for the high impedance Voltage Sensor
of figure 10.4. As part of the measurements, it was found that an AD8039 Dual OpAmp
has a slightly better common mode performance, i.e. less difference between amplifier
A1 and A2 in figure 10.4, than the same circuit with an AD8058 Dual OpAmp.
Unfortunately, the Spice model for the AD8038/8039 OpAmp is based on the single
AD8038, which has a "disable" input, and cannot be imported directly into Cadence AWR
DE. The specified performance of the AD8039 and AD8057 OpAmps is very similar,
however the quiescent current for the Dual AD8039 is 2 mA compared to 14 mA for the
Dual AD5058, so that the hardware can run longer from a 12V battery.
The "tuned" value of 219.2 Ω for unity gain was changed to 330 Ω to prevent overloads
due to the slight gain at higher frequencies as shown in figure 10.10. Figure 10.11 shows
the resulting hardware. A simple heatsink is used to conduct the heat from the AD 8017
output amplifier to the PCB and the instrument case.
Figure 10.11. Hardware of circuit of figure 10.4.
Amplifier protection
The OpAmps A1 and A2 of figure 10.4 operate from a ±5 V supply. The maximum
voltage at the input can thus be 10 V. Any larger voltages can damage the OpAmps. Since
RF Electronics: Design and Simulation
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