SNAA357 September 2022 LMX2820
LMX2820 RF output can be muted or unmuted through the MUTE pin. Direction of mute control is configurable with the PINMUTE_POL register bit (R77[8]). With one of the LMX2820 configured to active-high mute while the other LMX2820 is set to active-low mute, the user can use one mute control signal to ping-pong two LMX2820.
The RF switch takes the same mute control signal to pass the selected input channel RF signal to the output.
| GPIO Control Pin | PINMUTE_POL | LMX2820 Output | RF Switch Output |
|---|---|---|---|
| 0 | 0 (Active HIGH) | Unmute (Upper channel) | Upper channel |
| 0 | 1 (Active LOW) | Mute (Lower channel) | |
| 1 | 0 | Mute (Upper channel) | Lower channel |
| 1 | 1 | Unmute (Lower channel) |
Program the LMX2820 to different frequencies, the user can switch between two frequencies very fast.
With Instant Calibration, LMX2820 can change VCO frequency within a few micro-second. For details, see the Dramatically Improve Your Lock Time with VCO Instant Calibration application note. If the mute control signal has a period greater than 10 µs, the user has sufficient time to change the deselected LMX2820 output frequency during the mute period. Repeat programming LMX2820 in this way, the user can end up with a fast frequency sweep sub-system.