LG HB620 Service Manual page 37

3. TECHNICAL BRIEF
- RF switch
A RF switch allows the use of a single antenna input for all supported bands
- RXRF
RXRF consist of three parallel signal paths for different input bands, VHF, UHF and L-band.
Each path has an LNA, RFVGA and a WBD.
In UHF band, a notch filter improve the GSM compression up to 20dB. Depending on the sensitivity
loss, the DiB9080H can handle up to -15dBm GSM signal.
The function of the RFVGA is to amplify the signal after LNA while adding as little noise as possible.
It should be linear enough to handle all in-band interferes and GSM900 interferer.
The function of the WBD is to measure the amplitude on the output of RFVGA sio that the digital
baseband demodulator knows if or how far from compression RFVGA is.
- MIXER
The function of the MIXER is to down convert the signal from the radio frequency between 88MHz
and 1800MHz, to the baseband and performs channel selection. This is accomplished through the
selection of the LO frequency.
- Baseband
The baseband is a combination BBVGA and a high reject filter. The filter bandwidth is
programmable from 2 to 4 MHz. The gain is programmable in 0.13dB steps.
- LO
The PLL generates the LO I and Q signals needed for the down conversion.
- Crystal Oscillator
Crystal oscillator provides reference frequency for LO, DIGITAL and the system clock output for the
digital baseband demodulator.
- Bias
Bias block is based on a band gap voltage reference, voltage to current converter and a PTAT
current source for stable temperature behavior.
- ADC
This block samples the differential input analog signals. The maximum sampling frequency is
30MHz and the number of bits at both outputs of the ADC is 10.
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Only for training and service purposes