LG 512W Service Manual page 17

3. TECHNICAL BRIEF
The IF and RF output frequencies are set by programming the N Divider registers. All three PLL R
Dividers are fixed at R = 65 to yield a 200 kHz phase detector update rate from a 13 MHz reference
frequency.
Fout/N = Fref/65 (3.3)
For XIN = 13 MHz, Fout = N x 200 kHz
RF1 VCO(DCS)Frequency range : TX : 1,550 ~ 1,650 MHz, RX : 1,580 ~ 1,655 MHz
RF1 VCO(DCS)Frequency range : TX, RX : 1,150 ~ 1,185 MHz
IF VCO : 1,080 MHz
The RFOUT and IFOUT pins are driven by amplifiers that buffer the RF VCOs and IF VCO,
respectively. The RF output amplifier receives its input from either the RF1 or RF2 VCO, depending
upon which N divider register was last written to.
The RFOUT pin must be coupled to its load through an ac coupling capacitor. A matching network is
required to maximize power delivered into a 50 Ω load. The network is made to provide an adequate
match to an external 50ohm load for both the RF1 and RF2 frequency bands. The matching network
also filters the output signal to reduce harmonic distortion.
The RF output power is controlled with the RFPWR bit in register 0. Setting this bit increases the
supply current by approximately 1.2 mA.
The IFOUT pin must also be coupled to its load through an ac coupling capacitor. A matching
network is also required in order to drive a 50 Ω load.
Depending on transceiver requirements, the matching network may not be needed.
Figure 3-4. Synthesizer Circuit.
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