2010 IEEE 26-th Convention of Electrical and Electronics Engineers in Israel
Low Phase Noise Synthesizer
With Integral FM Modulator
Kuti Josefberg
FWI Ltd POBox 5870
Herzlia 43100 Israel
kuti@fwikj.com.
Chen Lev
AFEKA Tel Aviv Academic
College of Engineering
38 Mivtza Kadesh Tel Aviv
69107 Israel
Abstract – A low noise synthesizer combined with an analog FM
modulator had been implemented and tested successfully at 2.5 – 2.8
GHz. The modulating signal at 300-3000 Hz range had been ejected
into the LPF loop. The choice of the LPF components plays a major
role in the output spectral purity.
Index Terms – Synthesizer, Phase Lock Loop, FM Modulator
Ely Levine
AFEKA Tel Aviv Academic
College of Engineering
38 Mivtza Kadesh Tel Aviv
69107 Israel
ElyL@afeka.ac.
offset) and low phase noise (lower than -80 dBc/Hz at 1 kHz
offset). Due to iterative and prudent design of the filter, using
the suggested simulation tool of ANALOG DEVICES, and
with careful choice of the passive components for the
evaluation board, these requirements had been fully achieved.
The key element was to proceed step by step with the
simulated results and the measured validation.
I. INTRODUCTION
A frequency synthesizer is an essential component in many
communication systems, both wired and wireless. The special
case of a fixed frequency synthesizer combined with an
integral FM modulator had been suggested in past years but in
fact, there are no publications that describe high quality
experimental results for such a device. In this paper we present
the design steps and the measured results of a synthesizer with
integral FM modulator, based on commercial evaluation board.
II. BLOCK DIAGRAM
A general view of the evaluation board is given in figure 1. A
block diagram of the synthesizer is shown in figure 2 and
detailed description of the board is shown in figure 6. The role
of the PLL is to stabilize and control the center frequency. We
have focused here on a center frequency of 2.8 GHz although
the original range of the board was 5.75 - 5.9 GHz and larger
bandwidth is possible. The loop filter is the key component in
the design because it provides the spectral purity of the signal
and serves as the input port for the modulating signal.
III.
DESIGN CONSIDERATIONS
The main goal of our study was to design an FM modulator,
with input message at 300-3000 Hz within the PLL, while
keeping suppressed spurious (lower than -70 dBc at 1 MHz
978-1-4244-8682-3/10/$26.00 ©2010 IEEE
Figure 1 The ANALOG DEVICES ADF 4106EB1
evaluation board.
IV. PHASE NOISE AND FM MODULATION
The phase noise simulation for the final choice of the filter
components is shown in figure 3. Measured results are given in
figures 4-5. The procedure to measure the phase noise is as
follows: (1) measure the center frequency amplitude (2)
measure the SSB phase noise (3) subtract the SSB noise from
the center frequency amplitude and then subtract the bandwidth
resolution of the spectrum analyzer. A detailed example is
given in figure 5, where we see an excellent performance at
Modulating
Signal
Reference
Signal
Vmx 200-016
ADF4106
Phase
Detector
LPF
VCO
2.8 GHz
RF output
PC
Interface
Figure 2 A Block diagram of the PLL synthesizer
with FM modulator
offset of 10 kHz. At larger offsets the internal noise floor of the
spectrum analyzer masks the phase noise and thus we see big
differences between the simulations and the measurements as
shown in table 1. The FM modulation performances are
demonstrated in figures 7-10. Figure 7 shows a clean spectrum
for low level 10 kHz FM signal and figures 8-10 show the
specific Bessel spectra for 1 kHz FM signal with different
input voltages.
Phase Noise at 2.80GHz
-60
Total
Loop Filter
Chip
Ref
VCO
-70
Phase Noise (dBc/Hz)
-80
-90
SPAN = 100 kHz
-100
-110
Figure 5 Spectrum analysis of the CW signal at 2.8 GHz
-120
-130
-140
-150
-160
100
1k
10k
100k
1M
Frequency (Hz)
Figure 3 Simulated spectrum of the phase noise
offset = 10 kHz
VBW = 30 Hz
RBW = 1 kHz
CFrq Amp= -10.6 dBm
SSB Phase Noise@10kHz= -62.3 dBm
∆Amp = SSB Phase Noise - CFrq Amp = -72.9 dBm
10 Log (BWR)= 10 Log1000 = 30 dB
Phase Noise Amp = ∆Amp-10 Log (RBW) = -103 dBc/Hz
Offset
100Hz
1kHz
10kHz
100kHz
1MHz
100Hz
1kHz
10kHz
100kHz
1MHz
Figure 4 Measured spectrum of the phase noise
(lower than -82 dBc/Hz at 1 kHz offset).
Phase Noise
Measurement
-75 dBc/Hz
-82 dBc/Hz
-103 dBc/Hz
-117 dBc/Hz
-128 dBc/Hz
Phase Noise
Simulation
-88 dBc/Hz
-84 dBc/Hz
-112 dBc/Hz
-152 dBc/Hz
-195 dBc/Hz
Table 1 Simulated and Measured phase noise.
Figure 6
Detailed description of the board
Figure 7 Measured spectrum of the modulated signal
with low level FM at 10 kHz (spurious lower
than -70 dBc at 1 MHz offset). Span is 22 kHz.
Figure 10 Measured spectrum of the modulating signal
0.03V at 1 kHz. Span is 20 kHz.
V. CONCLUSION
A low noise synthesizer (-82 dBc/Hz at 1 kHz) at 2.5-2.8 GHz
with low spurious emission (-70 dBc @ 1 MHz offset)
combined with integral analog FM modulator (0.3-3 kHz) had
been demonstrated on the evaluation board Analog Devices
ADF4106EB1. The spectral purity complies with simulations
due to a prudent choice of the loop filter components.
REFERENCES
[1]. LMDS Evaluation Board For PLL Frequency Synthesizer,
EVAL-ADF4106EB1 Data Sheet, Analog Devices,
http://rapidshare.com/files/418512132/EVAL-ADF4106EB1.pdf
Figure 8 Measured spectrum of the modulating signal
0.001V at 1 kHz, Span is 10 kHz.
[2]. PLL Frequency Synthesizer, ADF4106 Data Sheet,
Analog Devices,
http://pdf1.alldatasheet.com/datasheetpdf/view/48641/AD/ADF4106.html
[3]. VCO Voltage Controlled Oscillator, UMX-200-D16 Data Sheet,
U.S. Microtech Inc,
http://www.datasheetdir.com/go/-xkj-bnm-xvkxnv.pdf
[4]. LOW PROFILE TCXO, FOX801BE
Data Sheet, FOXE lectronics,
http://w5jgv.com/vctcxo/fox801be.pdf
[5]. Phase-Locked Loops for High-Frequency Receivers and
Transmitters – Part 1&2, Analog Devices,
http://www.analog.com/library/analogDialogue/archives/3303/phase/index.html
http://www.analog.com/library/analogDialogue/archives/3305/phase_locked/index.html
Figure 9 Measured spectrum of the modulating signal
0.01V at 1 kHz. Span is 10 kHz.
[6]. Wide bandwidth frequency modulation of phase lock loops
www.rfdesign.com,
http://rapidshare.com/files/336797389/0200Rosemarin24.pdf.html
[7]. Agilent AN 1303 Spectrum Analyzer Measurements and
Noise Application Note
http://rapidshare.com/files/418511917/noise_measurements_using_a
spectrum analyzer.pdf