3GPP 38.300 v19.3.0 — the document's own text
5.4.4 Low band carrier aggregation via switching
Taught in 2. The six working groups and the line between them (TSG RAN — the group that specifies the radio, overview), 2. The six groups, and what each one worries about (TSG RAN — the group that specifies the radio, quick start).
In CA with low band spectrums of FDD carrier and supplementary DL (SDL) carrier, a UE may be configured with switching pattern between transmitter and receiver on FDD carrier used for PCell and receiver on SDL carrier used for an SCell.