SKY73134 Datasheet, PDF (3/17 Pages) Skyworks Solutions Inc. – Wideband PLL Frequency Synthesizer

PRELIMINARY DATA SHEET • SKY73134 FREQUENCY SYNTHESIZER
Functional Description
The SKY73134 is comprised of seven main functional blocks:
1. N-divider
2. R-divider
3. Phase detector
4. Charge pump
5. VCO and digital frequency VCO calibration
6. VCO dividers
7. Lock detect
N-Divider
The N-divider consists of a 64/65 prescaler, 12-bit main counter,
and 6-bit swallow counter. The 18 bit N-divider ratio is calculated
as:
N=P×M–S
Where: P = Prescaler value
M = Main counter value
S = Swallow counter value
The N-divider range is from P² – P to 2¹⁸, or it can vary from 4096
to 262144. For the 4 GHz VCO output, the minimum and
maximum comparison frequency are defined as:
FCOMP_MIN = VCO/NMAX = 4/2¹⁸ ≈ 15 kHz
FCOMP_MAX = VCO/NMIN = 4/4096 ≈ 977 kHz
R-Divider
The 11-bit programmable R-divider divides the reference input
frequency and generates the reference input for the phase
detector. The R-divider range varies from 1 to 2¹¹ (2048).
Since FCOMP= FREF/R-divider for a comparison frequency of
100 kHz, the maximum reference frequency could be 204.8 MHz.
Phase Detector
The phase detector is an edge-controlled digital circuit. The
circuit has two inputs: the reference signal (Ref) and the N-divider
output. There are two digital outputs (Up and Dn) that drive the
charge pump.
When the input phase difference is positive, the Up output is
pulled up to VDD. When the input phase difference is negative,
the Dn output is pulled down to ground. This type of phase
detector acts only on the positive edges of the input signals.
Charge Pump
The charge pump is used to convert the logic levels of the Up and
Dn pulses, carrying the phase error between the reference and
the divided signal into analog quantities/current pulses.
The output of the SKY73134 charge pump is programmable and
varies between 0.9 mA and 5.4 mA. Additional adjustment of the
charge pump current can be accomplished by changing the value
of the external PLL bias resistor.
VCO and Digital Frequency VCO Calibration
The SKY73134 incorporates four VCOs. Each VCO covers a
different frequency range between 2.7 and 6.0 GHz:
x VCO 1: 2.7 to 3.4 GHz
x VCO 2: 3.3 to 4.2 GHz
x VCO 3: 3.8 to 4.8 GHz
x VCO 4: 4.7 to 6.0 GHz
The VCOs are designed to generate the LO signal with the tuning
function controlled by the synthesizer. Each VCO uses a switch
capacitor array and an analog varactor for digital tuning. The
digital auto-tuning loop provides the proper 7-bit coarse tuning
setting for the VCO switch capacitors. This sets the oscillation
frequency as close to target as possible before starting fine
analog tuning.
When VCO auto-tuning is enabled, the PLL performs a seven-step
successive approximation process to digitally tune the VCO close
to the final programmed frequency. Once that is complete, analog
tuning is enabled to lock the VCO to the programmed frequency.
The auto-tuning loop is designed to compensate process variation
so that the VCO fine tuning range can be reduced to cover
temperature variation only. It significantly reduces VCO gain (Kv),
which reduces the VCO phase noise. This ensures that the PLL is
always locked.
VCO Dividers
The divider chain consists of dividers and LO drivers. Any VCO can
be divided by 2, 3, 4, or 8, which improves the LO phase noise by
6 dB, 9.5 dB, 12 dB, and 18 dB, respectively.
Using frequency division, the overall VCO range of the device is
widened from 0.34 to 6.0 GHz.
The output RF buffer has a programmable current that provides
variation in the output RF level from –4 to +4 dBm. The direct
non-divided VCO output can be monitored at the additional
bidirectional internal/external VCO pins. The divider chain and the
internal PLL can be locked by an external VCO.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201199A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 15, 2009
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