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CC430 Signal Chain: MAGA, LNA, LNA2, and DVGA
Is there a diagram of the CC430 radio core signal chain?
MAGA: I can set target amplitude from channel filter with MAGA_TARGET. The datasheet implies a higher setting improves sensitivity but increases the risk of either saturation or excessive gain reduction (blocking) in the presence of a strong signal elsewhere on the band.
LNAs 1 and 2: I can limit the sum of the gains of LNAs 1 and 2 using MAX_LNA_GAIN. I can control how the AGC dials them back using AGC_LNA_PRIORITY.
DVGA: I can limit this gain using MAX_DVGA_GAIN.
Is there a diagram showing the receive chain so if I cannot resist the urge to play with the knobs at least I'll know what I'm doing.
We do not provide detailed diagrams of the radio core. Sorry about this.
MAGN_TARGET sets the signal power level into the demodulator. If this is set too low the demodulator will have too small SNR to demodulate correctly. If you set it much higher than required for demodulation, the gain in the frontend will be higher than required (for strong signals) and hence blockers will also be amplified more than necessary impacting the selectivity/blocking.
The DVGA is included in the demodulator to reduce the required word lengths and thereby reduce the area. The DVGA is really just a 10 bit subset of a 17 bt wide word. Maximum DVGA gain uses 10LSB's and minimum DVGA gain uses 10MSB's. The MAX_DVGA_GAIN puts limits on the maximum gain. When using MAX_DVGA_GAIN =! 0 you limit the maximum DVGA gain and hence the switching activity.
The LNA gain can be reduced from maximum. This reduces the current consumption in "listening mode" when there is no signal at the antenna as the CC430 will always start at maximum gain and only reduce the gain if there is a (strong) signal at then antenna.
The AGC will adjust the analog gain (LNA1 +LNA2) depending on the input power level. When AGC_LNA_PRIORITY =’1’ the AGC will turn LNA1 gain to its minimum (3 gain settings) before it starts adjusting the LNA2 gain (8 gain settings). When AGC_LNA_PRIORITY =’0’ the AGC will turn LNA2 gain down to its minimum before it starts adjusting the LNA1 gain.
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