ST87M01 GNSS DC Block: 1nF vs 100pF for L1-Band Performance

[AndreasC]

Hello,

I am reviewing the reference design for the ST87M01 and noticed that a 1nF capacitor is specified for the DC block on the GNSS RF path.

In many high-sensitivity GNSS designs, 100pF is the standard choice for the 1.5 GHz L1 band to ensure the Self-Resonant Frequency (SRF) remains well above the operating frequency.

Questions:

1. Why was 1nF selected for this specific SiP instead of the typical 100pF?
2. Does the internal matching of the ST87M01 rely on the specific reactance of a 1nF series capacitor at 1575 MHz?
3. For a design strictly optimized for GNSS sensitivity, would a 100pF High-Q (C0G) capacitor offer any measurable improvement in insertion loss or noise figure compared to the 1nF reference value?

Greetings,

Andreas

[mbarg.1 · Accepted solution]

AS you told, it is a DC block - not part of a resonant circuit - any near-zero impedence will not alter impedence and RF performances - more important could be capacitor size and position.