Boost power supply and high voltage DAC provide tuning signal circuit diagram for BST capacitor

The circuit shown in Figure 1 generates a high-voltage signal that controls the capacitance of a B ST (barium strontium titanate) capacitor . The BST capacitance can be changed simply by applying voltages between 0 V and 30 V to the correct terminals. In this way, the dielectric thickness changes and therefore the capacitance changes. BST is commonly used in tunable antenna arrays and tunable filters. There are clear advantages especially for these tuning applications, such as compensation of component tolerance errors, fine tuning of filter cutoff frequencies or network impedance matching for tunable antennas.

Figure 1. Boost power supply and high-voltage DAC provide tuning signal to B ST capacitor (simplified schematic: not all connections shown)

Such applications require a convenient, compact, low-cost circuit to generate high-voltage power, and it is often not practical to add a separate power supply just for this function. The circuit in Figure 1 meets these requirements using an ADP1613 boost converter and an AD5504 30 V/60 V DAC . The total board area of ​​the boost regulator circuit is only 43 mm2. The ADP1613 is available in an 8-pin MSOP package, and the AD5504 is available in a 16-pin TSSOP package.

Boost circuits can also be used in LED driver applications and to provide receiver bias voltages in optical communications systems.