High Voltage (30 V) DAC Powered from a Low Voltage (3 V) Supply Generates Tuning Signals for Antennas and Filters (cn0193)
The circuit shown in Figure 1 generates a high voltage signal that controls the capacitance of a BST (barium strontium titanate) capacitor. The capacitance of a BST capacitor can be altered by applying a voltage of between 0 V and 30 V to the correct terminal. This changes the thickness of the dielectric and, hence, the capacitance. BSTs are often used for tuning antenna arrays or tunable filters. Clearly, there is an advantage in being able to tune these applications—for example, compensating for component tolerance errors, fine tuning the cutoff frequency of a filter, or network impedance matching for tunable antennas.
This application requires a convenient, compact, and low cost circuit to generate the high voltage power supply because it is often not practical to add a separate supply simply for this function alone. The circuit in Figure 1 meets these requirements using the ADP1613 boost converter and the AD5504 30 V/60 V DAC. Total board area for the boost regulator circuit is only 43 mm2. The ADP1613 is available in an 8-lead MSOP package and the AD5504 in a 16-lead TSSOP.
The boost circuit can also be used in LED driver applications and to supply receiver bias voltages in optical communications systems.
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