VCO
PFD
=
x PLL DIV x NINT
f
f
VCO
PFD
25
NFRAC
=
x PLL DIV x NINT +
2
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f
f
PLL_DIV_SEL
PLL DIV = 2
REF
PFD
=
RDIV
f
f
REF
VCO
25
NFRAC
=
x PLL DIV x NINT +
RDIV
2
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f
f
36
SLWS245B – MAY 2014 – REVISED FEBRUARY 2017
Product Folder Links:
Copyright © 2014–2017, Texas Instruments Incorporated
8.3 Feature Description
8.3.1 RF Output
The RF output is single ended and can drive a 50-
Ω
load. It can be tuned with the use of an output matching
network to optimize the linearity and return loss performance within a selected band.
8.3.2 Baseband Inputs
The baseband inputs consist of the in-phase signal (I) and the quadrature-phase signals (Q). These I and Q
signals are differential. The baseband lines are nominally biased at 0.25-V common-mode voltage (V
CM
);
however, the device can operate with a V
CM
in the range of 0 V to 0.5 V. The baseband input lines are normally
terminated externally 50
Ω
on TRF3722 evaluation board, though it is possible to modify this value if necessary
to match to an external filter load impedance requirement.
8.3.3 LO Output
The LO outputs are open collector differential outputs and are biased externally. These differential outputs can
be tuned to optimized output power along with OUTBUF_BIAS register settings. It also is possible to use LO
outputs in single ended mode.
8.3.4 PLL Architecture
illustrates a block diagram of the PLL architecture.
The VCO output frequency (f
VCO
) is given by
:
(1)
(2)
(3)
(4)
Where f
REF
is the reference input frequency, RDIV is the reference divider division ratio and the phase -
frequency detector frequency is f
PFD
. PLL_DIV_SEL controls the division ratio of the programmable divider (PLL
DIV) before the dual-modulus prescaler (DMP). NINT and NFRAC/2
25
is the integer and fractional part of the
fractional divider (N.f), respectively. In Integer mode, the fractional setting is ignored and
is applied.
(5)
The complete feedback divider block consists of a PLL DIV, DMP, and N.f. The prescaler can be programmed as
either a 4/5 or an 8/9. N.f includes an
A
and
M
digital counters.