Detailed explanation of filter circuit design and scheme

The design of LTCC filter is usually based on the classical filter design theory. In terms of structure, there are two main structures: one is the traditional LC resonant unit structure, which is composed of capacitance and inductance with lumped parameters, and the other is the multi-layer coupling stripline structure. The low-pass filter designed in this paper adopts the first lumped parameter form, and the circuit schematic diagram of the idealized low-pass filter is shown in Figure 3.

The capacitance and inductance of the lumped parameters in the LTCC filter designed in this paper are integrated in the ceramic substrate through LTCC multilayer ceramics. There are two ways to design the embedded capacitor in LTCC: vertical interdigital (VIC) capacitor and metal dielectric metal (MIM) capacitor. The filter designed in this paper uses vertical interdigital (VIC) capacitor as the embedded capacitor. Under the same capacitance, Vic structure capacitor can greatly reduce the end electrode area compared with MIM structure capacitor, thus effectively reducing the filter size.

　　There are plane spiral inductor, stack spiral inductor and multi-layer spiral inductor in LTCC. The low-pass filter designed in this paper adopts multi-layer spiral inductor. Under the same effective inductance, this structure has higher self resonance frequency and quality factor than plane spiral and stack spiral inductors.