Motorola V975 Service Manual

Motorola Confidential Proprietary
Theory of OperationService Manual(Level 3)
3-11
Draft 1.0
MC13786 (U200)
The MC13786 is an integrated I/Q modulator, IF and
RF variable gain amplifier, UHF frequency synthesizer
with a fully integrated VCO, image-reject upconverter
mixer, and linear PA driver.
The synthesizer or phase locked loop (PLL) consists of
a buffer amplifier, multi-modulus prescaler (divide by 4,
5, 6, and 7), a sixbit programmable post divider, refer-
ence divider, phase detector, and charge pump. The
PLL uses a reference frequency of 15.36 MHz. One
frequency synthesizer/VCO provides both the main and
offset LO functions. The VCO operates over a fre-
quency range of 2114 MHz to 2263 MHz and is fully
integrated.
The I/Q Modulator consists of a quadrature generator
and two Gilbert Cell active mixers. Using the offset LO
and quadrature generator, the active mixers modulate
the differential baseband I/Q signals onto a TXIF sig-
nal. Depending on the channel selection, the TXIF fre-
quency will range from 274 MHz to 283 MHz.
From the active mixers, the TXIF signal is fed into a IF
Variable Gain Amplified (IF VGA). The IF VGA has
70 dB of total typical gain control range and is con-
trolled by the VGC line. The output of the VGA shall
have a single pole bandpass tank circuit to provide at-
tenuation to far-out noise.
The upconverter has an image-reject configuration so
that the unwanted sideband is rejected to decrease the
linearity requirements of the VGA stage. An input
polyphase filter shall provide the necessary phase shift
for the IR mixer. The TXIF signal is upconverted to a
TX carrier frequency ranging from 1920MHz to
1980MHz. An on-chip copper balun shall provide the
differential to single ended conversion necessary for the
following stages.
The VGA provides a reduction in gain and current to
optimize the TX lineup for lower output power levels.
The PA driver amplifies the signal to provide sufficient
drive for the radio power amplifier.
/2 FracN
TANK
LP
RATTLER
MIXERMIXER
VGC
VGC
VCO
BB_QX
BB_Q
BB_IX
BB_I
PS_CLK_RAT
RAT_VCA_AOC
TX_EN
RATTX_OUT
Figure 3-14. Rattler (U200)
RF WCDMA Transmitter

Motorola V975 Specifications

General

Brand	Motorola
Model	V975
Category	Cell Phone
Language	English