Motorola A840 Service Manual page 24

Theory of Operation
Figure 8. RFL6000 Block Diagram
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The RFL6000 IC includes two LNA circuits, one optimized for the Cellular band
and one for PCS. The LNAs are separated from all other receive functions contained
within the RFR6000 receiver IC to improve mixer LO to RF isolation – a critical
parameter in the Zero-IF architecture. Isolation is further improved using high
reverse isolation circuits in the LNA designs.
The RFL6000 is a multi-band multi-mode IC:
Bands:
• Cellular bands
• PCS bands
Modes:
• AMPS-FM
• CDMA (known as IS-95, cdmaOne, IS-98, cdma2000, 1xEVDO)
The two LNAs are dedicated to different frequency bands; the CLNA supports
Cellular bands while the PLNA supports PCS bands. The PLNA gain is always
controlled via the Serial Bus Interface (SBI) with three valid settings: Max, Mid,
and Low. Three CLNA gain states are also controlled via the SBI for CDMA signal
reception, but only two gain states are available for FM operation (Max and Low).
When operating in the Cellular-FM mode, the CLNA gain is controlled by a
dedicated MSM signal applied to pin 6 (FM_STEP) rather than the SBI.
The IC operating mode and LNA bias currents are automatically adjusted via
software to minimize DC power consumption. The IC is placed in Sleep, Rx, and
Rx/Tx modes depending upon the handset's status, with LNA bias current also
adjusted to meet RF performance requirements with minimal power dissipation
when active.
The device is fabricated using a SiGe BiCMOS process ideally suited for high-
performance RF circuits and digital I/O functions. All analog/RF functions operate
off a common supply voltage (VDDA), with the digital I/O circuits operating off a
separate supply (VDDM). VDDM is connected to the MSM_PAD voltage to assure
compatibility across the digital interface and prevent latch-up conditions.
The RFL6000 IC is packaged in a very small 16-pin bump chip carrier (16 BCCP)
that includes a center slug for soldering directly to PCB ground. This provides
excellent RF grounding, mechanical strength, and a solid thermal path.
June 07, 2004
A840