SKY73100-11_09 Datasheet, PDF (10/21 Pages) Skyworks Solutions Inc. – 865-960 MHz High Performance VCO/Synthesizer

DATA SHEET • SKY73100-11 VCO/SYNTHESIZER
Lock Detect
Lock detection circuitry provides a CMOS logic level indication
when the PLL is frequency locked (high when locked). Normally,
pin 22 (LD) is used for lock detect output. This pin can also be
programmed as the R1 divider output, N-divider output, or DPLL
test output. Pin 22 is controlled by Word 0, bits [17:15].
Reference Input Divider
The R-counter (reference input clock divider) consists of three
divide-by-two blocks and one multiplexer controlled by the
rdiv[3:2] parameter in Word 2. The R1 divider is used to select a
divide-by-one, two, four, or divide-by-eight function.
The integral loop filter (see Figure 1) is designed to operate at an
internal comparison frequency of approximately 6.5 MHz. The
input reference signal must be divided using the rdiv [3:2] bits in
Word 2 to closely match this frequency. Further optimization of
the loop filter bandwidth may be accomplished using the
cp_output [4:2] bits in Word 0.
Reference Buffer Bandwidth
The two-bit parameter ref_bw_sel adjusts the operating point of
the input buffer to compensate for different reference signal
sources. Generally the best setting is 50 MHz, but this could vary
depending on the source used.
Synthesizer Output Switch
An on-chip switch is integrated into the SKY73100-11 RF output
after the balun and is controlled by the SW_EN signal (pin 4) as
indicated below:
SW_EN Input
High
Low
Synthesizer Output
On
Off
The switch provides >50 dB isolation at the synthesizer RF
output. This allows the SKY73100-11 to be used for GSM
applications.
Synthesizer Programming
To program the synthesizer to the correct frequency, values for
the N-counter (both M and A portions), fractional divisor (FN), and
fractional modulus extender (ME) are needed. These values are
used to determine the total divider ratio, D_Total, according to
Equation 1:
D_Total = N_actual + FN_actual + ME_actual + 3.5
(1)
Where: N_actual = the actual value of the N-counter
FN_actual = the actual fractional divisor
ME_actual = the actual fractional modulus extender
Because of the way the ∆Σ modulator is implemented in the
SKY73100-11, the number 3.5 must be added to the division
number to obtain the final division ratio.
The calculated value for D_Total can then be used to determine the
correct synthesizer frequency, RF:
RF =
F_REF
R1
× D_Total
(2)
Where: F_REF = the reference frequency
R1 = the reference divider radio
The 6-bit M-counter and the 4-bit A-counter portions of the N-
counter are calculated according to the following relationships:
N_actual is the actual N-counter value and is the integer portion of
(D_Total – 3.5):
N_actual = M_actual × P + A_actual
(3)
If: M = M_actual (binary number, fit to six bits)
A = A_actual (binary number, fit to four bits)
Then: N = M × 2⁴ + A
Where: N is the number to be programmed into the N-counter.
The synthesizer has a selectable prescaler of 8/9 or 16/17. If the
16/17 prescaler is used:
P = 2⁴ = 16
In this case, N is the same as N_actual, M is equal to the six MSBs of
N_actual, and A is equal to the four LSBs of N_actual.
If the 8/9 prescaler is used:
P=8
Here, N is not equal to N_actual. The A-counter portion only uses the
three LSBs (the 4^th bit of the A-counter is a “don’t care” bit).
NOTE: The minimum actual N counter value for the 8/9 mode is
8 x 7 = 56, and for the 16/17 mode is 16 x 15 = 240.
The fractional divisor code (FN) sets the fractional-N modulo up to
256 modulo according to the following equation:
FN _actual
=
D_{7 ⎜⎜⎝⎛}
1
2
⎟⎟⎠⎞
+
D_{6 ⎜⎜⎝⎛}
1
2²
⎟⎟⎠⎞
+
D_{5 ⎜⎜⎝⎛}
1
2³
⎟⎟⎠⎞
+
•
•
•
+
D_{0 ⎜⎜⎝⎛}
1
2⁸
⎟⎟⎠⎞
(4)
The value of FN is equal to the binary representation of 256 (or 2⁸)
× FN_actual, or:
FN = D₇ × 2⁷ + D₆ × 2⁶ + D₅ × 2⁵+ . . . D₀
The fractional modulo can be extended up to 2²³ using the modulo
extender (ME) if required:
ME_actual = D₁₄(1/2⁹) + D₁₃(1/2¹⁰) + D₁₂(1/2¹¹) + . . . + D₀(1/2²³)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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April 15, 2009 • Skyworks Proprietary and Confidential Information • Products and Product Information are Subject to Change Without Notice • 200361B