Motorola E685, Service Manual, Page: 27 / 97

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reception frequency for cellular system terminal equipment while remove other signals and image
components within passband for the purpose of eliminating the noise in the receiver. It has an
Insertion loss of maximum 2.5[dB].
4. RFR6120 (IC100)
The RFR6120 is a RF-to-Baseband receiver IC, an integral component of Zero-IF chipset. The
RFR6120 IC provides the Zero-IF receiver signal path that consists of an LNA and I/Q down-
converters for cellular-CDMA mode handsets.
The cellular receiver path consists of a four-stage variable-gain LNA, an external RF filter with
single-ended input and differential output, a pair of RF-to-Baseband inputs (configured
differentially with two-stage gain adjustments). The down converted baseband signals are
multiplexed and routed to lowpass filters.
The RFR6120 IC includes substantial LO generation and distribution circuitry. Both the cellular and
GPS LO signals originate within the on-chip VCOs that are closed-loop controlled by the
RFT6120’s Rx PLL via the VCO_FTUNE pin(only one VCO is active at a time).
Pin 6 (R_BIAS) connects an external resistor that adjusts several RFR6120 IC internal bias
currents; an 11.3 kΩ, 1% resistor must be connected between this pin and ground. Pin 38
(RCLNA) connects to a 5.76 kΩ, 1% resistor between the pin and ground to adjust the LNA bias
current. An AC-coupled 19.2 MHz reference is required at pin 27 (TCXO).
All control and status commands are communicated through the RFR6120’s MSM-compatible 3-
line Serial Bus Interface (SBI), allowing efficient initialization, control of device operating modes
and parameters, verification of programmed parameters, and status reports.
7. VC-TCXO (Voltage Controlled Temperature Compensated Crystal Oscillator) : TCO-
5871 (TCO100)
This is reference frequency source needed for operating mobile station system. Its frequency is
19.2MHz, which is applied to RF parts and MSM.