Simple Amplitude and Phase Detector for
Accelerator Instrumentation
K. H. Hu, Jenny Chen, C. H. Kuo, Demi Lee, K. T. Hsu
Synchrotron Radiation Research Center
No. 1 R&D Road VI, Hsinchu Science-Based Industrial Park, Hsinchu, Taiwan.
Abstract. Amplitude and phase are important parameters of an RF system and beam properties.
Commercial RF/IF gain and phase detector chip can be simply used to extract amplitude and phase
information. This detector can measure the amplitude log ratio and phase difference between OR of
two RF signals simultaneously. The method is simpler to implement than other methods. Design
consideration and implementation details will be discussed in this report. Preliminary test results and
possible applications will be summary in this report.
INTRODUCTION
Amplitude and phase properties of RF system and charge particle beam are
important parameters of an accelerator system. Rich information is embedded in
these two parameters. The standard method to measure phase and amplitude are done
by two-separated detectors, an amplitude detector and a phase detector [1].
Quadrature signal processing by using I/Q detection techniques has been widely used
in sophisticated applications [2] recently. This method can provide precision
measurement, but with complicated circuitry and occupying much space. Most
precision phase detectors do not work at the RF frequency. It needs an RF
down-conversion or direct RF sampling process. It is too complicated for some
applications.
The newly released commercial RF/IF gain and phase detector chip, AD8302
provides a simple way to measure amplitude log ratio and the phase difference of two
RF signals simultaneously [3]. Its features include very few components and a wide
frequency working range. The log amplifier has been reported to work with S band
for BPM applications [4,5]. Direct working at an RF frequency up to the S band is
possible for the detector. It provides a convenient way to implement simple amplitude
and phase detection circuitry for accelerator applications.
AMPLITUDE AND PHASE DETECTOR
Commercial chip AD8302 is adopted to implement amplitude and phase detector,
working at the RF frequency directly. Figure 1 shows a functional block diagram of
the detector. The chip includes a closely matched pair of demodulator logarithmic
amplifiers and a phase detector. The amplitude demodulator consists of seven stages
of 60dB log-ratio amplifiers. The phase detector is of the multiplier type. It requires a
CP648, Beam Instrumentation Workshop 2002: Tenth Workshop, edited by G. A. Smith and T. Russo
© 2002 American Institute of Physics 0-7354-0103-9/02/$19.00
523
few external
external components,
components, has
has an
an input
input range
range from
from -60dBm
–60dBm to
to 0dBm,
0dBm,
measures
gain
few
OdBm, measures
measures gain
gain
few
external
components,
–60dBm
and phase
phase up
up to
to 2.7GHz,
2.7GHz, normal
normal gain
gain sensitivity
sensitivity of
of 30mV/dB,
30mV/dB,
typical
gain
and
30mV/dB, aaa typical
typical gain
gain
and
phase
nonlinearly << 0.5
0.5 dB,
dB, normal
normal phase
phase sensitivity
sensitivity of
of
10mV/Degree,
typical
phase
nonlinearly
of 10mV/Degree,
lOmV/Degree, aaa typical
typical phase
phase
nonlinearly
nonlinearly <1
<1 Degree,
Degree, and
and aa fast
fast response
response time.
time. These
These characteristics
characteristics
support
the
nonlinearly
characteristics support
support the
the
nonlinearly
easy
detection
of
amplitude
and
phase
information.
easy
amplitude and
and phase
phaseinformation.
information.
easy detection
detection of amplitude
RF Detector
Detector for
for Gain
Gain &
& Phase
Phase Measurement
Measurement
RF
InputA
A
Input
A
Input
60 dB
dB Log
Log Amps
Amps
60
(7 Detectors)
Detectors)
(7
Video
Video
Output
Output
A
A
++
Σ
Σ
--
++
Gain
Gain
Gain
Output
Output
Output
Σ
Σ
--
Gain
Gain
Offset
Offset
Phase
Phase
Offset
Offset
InputB
B
Input
B
Input
60 dB
dB Log
Log Amps
Amps
60
(7 Detectors)
Detectors)
(7
-++ Σ
Σ
Video
Video
Output
Output
B
B
Phase
Phase
Output
Output
FIGURE 1.
1. The functional
functional block diagram
diagram of AD8302.
AD8302.
FIGURE
FIGURE
1. The
The functional block
block diagram of
of AD8302.
April 16, 2002
April 16, 2002
A measurement
measurement system
system was
was setup
setup as
as show
show
in
Figure
to
determine
the
A
measurement
system
was
A
setup
as
show in
in Figure
Figure 222 to
to determine
determine the
the
performance
of
the
detector.
The
system
consists
of
reference
and
test
signal
input
performance of
of the
the detector.
detector. The
The system
performance
system consists
consists of
of reference
reference and
and test
test signal
signal input
input
arms. The
The coherent
coherent output
output of
of the
the RF
RF signal
signal generator
generator is
is
attenuated
to
provide
arms.
The
coherent
output
of
the
RF
arms.
signal
generator
is attenuated
attenuated to
to provide
provide
a
–30dBm
reference
signal
that
is
connected
to
the
reference
arm
input
of
the
detector.
–30dBm reference
reference signal
that is
aa -30dBm
signal that
is connected
connected to
to the
the reference
reference arm
arm input
input of
of the
the detector.
detector.
The output
output of
of the
the signal
signal generator
generator is
is then
then connected to
to the signal
signal arm of
of the detector.
detector.
The
The
output of
the signal
generator is
then connected
connected to the
the signal arm
arm of the
the detector.
Next,
the
signal
generator
is
operated
in
the
external
pulse
modulation
mode.
Next, the
the signal
signal generator
generator is
is operated
operated in
Next,
in the
the external
external pulse
pulse modulation
modulation mode.
mode.
Additionally,
a
voltage
controlled
phase
shifter
is
inserted
between
the
signal
Additionally, aa voltage
voltage controlled
controlled phase
phase shifter
Additionally,
shifter is
is inserted
inserted between
between the
the signal
signal
generator output
output and
and signal
signal input
input arm
arm of the
the detector for
for phase
phase detector
detector functionality
generator
generator
output and
signal input
arm of
of the detector
detector for phase
detector functionality
functionality
testing. This
This phase
phase shifter
shifter can
can be
be removed
removed or
or maintained at
at a constant phase
phase position
testing.
testing.
This phase
shifter can
be removed
or maintained
maintained at aa constant
constant phase position
position
to test
test gain
gain characteristics.
characteristics.
to
to test gain characteristics.
RF Detector
Detector for
for
RF
Gain &
& Phase
Phase
Gain
Measurement
Measurement
RF Signal
Signal Generator
Generator
RF
Attenuator
Attenuator
Coherent
Coherent
Output
Output
External
External
Pulse
Pulse
Modulation
Modulation
Pulse
Pulse
Generator
Generator
Gain
Gain
Output
Output
- 30 dbm
- 30 dbm
Voltage
Voltage
Control
Control
Phase
Phase
Shifter
Shifter
D.U.T.
D.U.T.
Oscilloscope
Oscilloscope
Oscilloscope
&
&
DVM
DVM
Phase
Phase
Output
Output
Function
Function
Generator
Generator
FIGURE 2. ADS302 amplitude and phase detector function test block.
FIGURE 2.
2. AD8302
AD8302 amplitude
amplitude and
and phase
phase detector
detector function
function test
test block.
block.
FIGURE
Figure 3 displays the amplitude function test results. When this detector is
Figure 33 displays
displays the
the amplitude
amplitude function
function test
test results.
results. When
When this
this detector
detector is
is
Figure
524
operated at
operated
at 500MHz,
500MHz, the
the amplitude
amplitude ac
ac performance
performance is
is shown
shown in
in Figure
Figure 3(a).
3(a). Figure
Figure
3(b) illustrates
illustrates that
that the
amplitude sensitivity
3(b)
the amplitude
sensitivity is
is 30mV
30mV at
at aa reference
reference power
power of
of -30
-30
dBm and
and an
input signal
power sweep
dBm
an input
signal power
sweep range
range from
from –60dBm
-60dBm to
to 0dBm.
OdBm. Phase
Phase function
function
test results
results are
test
are shown
shown in
in Figure
Figure 4.
4. The
The phase
phase ac
ac performance
performance is
is shown
shown in
in Figure
Figure 4(a).
4(a).
Figure 4(b)
4(b) illustrates
Figure
illustrates that
that the
the phase
phase sensitivity
sensitivityisis10
10mV/Degree.
mV/Degree.
Single Seq S.OOMS/s
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184mV
C1 Freq
Low signal
amplitude
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Low signal
amplitude
MlO.Ojas Ch2 J"
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17:08:33
33 (a)
(a) Amplitude
Amplitude modulation
modulation test
test results.
results.
2
1
1
1.8
1
1
1
1
1.6
Gain Output (Volt)
1.4
1
1.2
; *'
,*
1
0.8
t
0.6
^
0.4
0.2
0
-60
-60
•fa
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,-*-"
-50
-50
-40
-40
/
\
i_
i
i
i
i
i
i
-30
-30
Input
Input power
power (dBm)
(dBm)
-20
-20
-10
-10
0C
3(b)
3(b) The
The amplitude
amplitude sensitivity
sensitivity of
of detector.
detector.
FIGURE 3.
FIGURE
3. Amplitude
Amplitude sensitivity
sensitivity of
of detector
detector when
when input
input frequency
frequency is
is 500MHz.
500MHz.
PRELIMINARY
PRELIMINARY BEAM
BEAM TEST
TEST RESULTS
RESULTS
This amplitude
amplitude and
phase detector
This
and phase
detector can
can be
be used
used in
in various
various applications
applications involving
involving
machine physical
physical experiments.
experiments. Beam
machine
Beam transfer
transfer function
function measurement
measurement was
was used
used to
to
demonstrate the
the functionality
demonstrate
functionality of
of the
the detector.
detector. Figure
Figure 55 describes
describes the
the experimental
experimental
setup for
setup
for beam
beam transfer
transfer function
function measurement.
measurement.In
Inthis
thisexperiment,
experiment,the
theRF
RFphase
phasewas
was
525
ci Pk-Pk
356mV
C2. Freq
4S.S?532kH2
Unstable?
histogram
iddmV W "Ch2
LOO V '
M S.OOjas "Ch2 ' . / 1 . 3 4 V i May 2001
21:25:43
44 (a)
(a) The
The phase
phase modulation
modulation test
test result.
result.
1.05
1
P has e output (V )
0.95
~ 0.9
0.9
0.85
0.8
0.75
0.7
0
5
10
10
15
15
20
20
25
30
P has e s hift (Degree)
Phase shift (Degree)
44 (b)
(b) The
The phase
phase sensitivity
sensitivity of
of detector.
detector.
FIGURE 4.
FIGURE
4. Phase
Phase sensitivity
sensitivity of
of detector
detector when
when input
input frequency
frequency is
is 500MHz.
500MHz.
modulated near Ifs (synchrotron oscillation frequency) and the RF gap voltage
modulated
(synchrotron
frequency)signal
and was
the RF
gap voltage
modulation near
was 1fs
approximately
2fs.oscillation
The RF reference
connected
to the
modulation
was
approximately
2fs.
The
RF
reference
signal
was
connected
to the
reference arm of the detector to provide a reference for gain and phase measurement.
reference
of thefrom
detector
to provide
a reference
for gain
and phase
The beamarm
signal
the BPM
output
was passed
through
a 500 measurement.
MHz narrow
The
beam
signal
from
the
BPM
output
was
passed
through
a
500 MHzThe
narrow
bandwidth band pass filter and connected to the signal arm of the detector.
beam
bandwidth
band
pass
filter
and
connected
to
the
signal
arm
of
the
detector.
The
beam
transfer function was measured using a dynamic signal analyzer (DSA), working
in
transfer
function
measured
using
a dynamic
analyzer
working via
in
the DC-100
KHzwas
frequency
range.
This
DSA wassignal
connected
to a (DSA),
control network
the
KHz frequency
ThisThe
DSA
was connected
to a was
control
networkby
viaa
NTsDC~100
GPIB/ENET
100 bus range.
interface.
experiment
process
controlled
NI’s
GPIB/ENET
100
bus
interface.
The
experiment
process
was
controlled
by
a
MATLAB script, running on a control console. The phase modulation was applied to
MATLAB
script,
running
on
a
control
console.
The
phase
modulation
was
applied
to
the phase shifter on low level RF electronics (LLRF) and the gap voltage modulation
the
RF electronics (LLRF)
and on
the the
gap LLRF
voltagesystem.
modulation
wasphase
also shifter
appliedontolow
thelevel
voltage-controlled
attenuator
The
was
also
applied
to
the
voltage-controlled
attenuator
on
the
LLRF
system.
The
detector simultaneously outputs amplitude and the phase difference between beam
detector
signals. simultaneously outputs amplitude and the phase difference between beam
signals.
526
Beam
Beam Transfer
Transfer Function
Function Experiment
Experiment –– Measurement
Measurement Setup
Setup
^
499.654
499.654 MHz
MHz
Master
Master
Oscillator
Oscillator
Driver
Driver
-30
Source
Source
output
output
-35
-30
-40
-35
-45
-40
51.5
-40
-60
-80
-40
-100
-60
-120
-80
499.694
-100
-120
499.695
499.694
499.695
499.696
499.697
499.698
499.699
499.697
499.698
499.699
50
50.5
49.5
50
49
49.5
48.5
49
48
48.5
47.5
48
-50
-45
-55
-50
-60
-55
-65
-60
Phase
Phase Modulation
Modulation
Phase
Modulation
Or
Or
Or
Gap
Voltage
.Gap
Gap Voltage
VoltageModulation
Modulation
Modulation
-70
-65
-80
-75
500
-80
500
550
550
600
600
650
650
700
750
700
750
800
800
850
850
900
900
950
950
1000
RF
RF Reference
Reference
1000
499.7
Signal
Signal
Input
Input
GPIB/ENET 100
GPIB/ENET 100
Controller
Controller
Control
Control
Network
Network
Dipole
Dipole
Oscillation
Oscillation
-75
-70
499.7
47.5
499.696
Transmitter
Transmitter
Low
Level RF
RFElectronics
Electronics
Low Level
Level
RF
Electronics
(Amplitude
(Amplitude &
&Phase
PhaseControl)
Control)
(Amplitude
&
Phase
Control)
RF
RF
Distribution
istribution
Distribution
SRS
SRS 780
780
Dynamic
Dynamic Signal
Signal Analyzer
Analyzer
51
51.5
50.5
51
Beam
Beam
Beam
RF
RF Cavity
Cavity
Amplitude
Am
Amplitude Phase
Phase
Modulator
Shifter
Mo
Modulator
Shifter
AD8302
AD8302
Amplitude
Amplitude
&
&
Phase
Phase Detector
Detector
∆x
∆x
ΣΣ
Ethernet
Ethernet Switch
Switch
Fabric
Fabric
Quadrupole
Quadrupole
Oscillation
Oscillation
Hybrid
Hybrid
Junction
Junction
∆y
Ay
∆y
BPM
BPM
June
June 2,
2, 2001
2001
FIGURE 5.
FIGURE
5. Beam
Beam amplitude
amplitude and
andphase
phasemeasurement
measurementblock
blockdiagram.
diagram.
amplitude
and
phase
measurement
block
diagram.
Figure 66 displays
displays the
Figure
the magnitude
magnitude response
transfer function
function with
with
response of
of the
the beam
beam transfer
transfer
function
with
phase modulation.
modulation. Several
phase
were set.
set. Upward
Upward and
and downward
downward
Several modulation
modulation amplitudes
amplitudes were
were
set.
Upward
and
downward
sweeps were
were done
done in
sweeps
and 6(b)
6(b) summarize
summarize the
the
in the
the experiment.
experiment. Figures
Figures 6(a)
6(a) and
and
6(b)
summarize
the
preliminary
results.
The
phase
modulated
beam
transfer
function
shows
strong
preliminary results. The phase modulated beam transfer function
function shows
shows strong
strong
hysteresis,
which
hysteresis, which
which has
has been
been interpreted
interpreted in
in
several
reports
[6,7].
In
large
amplitude
hysteresis,
has
been
interpreted
in several
several reports
reports [6,7].
[6,7]. In
In large
large amplitude
amplitude
modulation,
the
beam
splits
into
two
beamlets,
which
oscillate
out
of
modulation, the
the beam
beam splits
phase.
The
dip
modulation,
splits into
into two
two beamlets,
beamlets, which
which oscillate
oscillate out
out of
of phase.
phase. The
The dip
dip
in
the
amplitude
spectrum
is
the
overall
response
to
this
effect.
in the
the amplitude
in
amplitude spectrum
spectrum isisthe
theoverall
overallresponse
responsetotothis
thiseffect.
effect.
6(a)
The frequency
upward sweep.
6(a)
6(a) The
The frequency
frequency upward
upward sweep.
sweep.
527
6(b) The
The frequency
frequency downward
6(b)
downward sweep.
sweep.
FIGURE 6.
6. Phase
Phase modulated
modulated magnitude
magnitude response
response of
of beam
FIGURE
beam transfer
transfer function
function in
in multi-bunch
multi-bunchoperation
operation
mode.
mode.
The storage
storage ring
ring of
of SRRC
SRRC is
is hindered
hindered by
by strong
coupled-bunch instabilities.
The
strong coupled-bunch
instabilities. Two
Two
existing
DORIS
cavities
are
the
major
sources
of
the
instability.
The
existing DORIS cavities are the major sources of the instability. The RF
RF system
system will
will
be upgraded
upgraded into
into aa superconducting
superconducting RF
RF (SRF)
(SRF) system
system in
be
in 2003.
2003. The
The project
project will
will adopt
adopt
CESR’s nearly
nearly high
high order
order mode
mode (HOM)
(HOM) free
free SRF
CESR's
SRF cavity
cavity to
to eliminate
eliminate longitudinal
longitudinal
coupled
bunch
instability
and
double
the
stored
beam
current
coupled bunch instability and double the stored beam current (400
(400 mA).
mA). Before
Before the
the
upgrade,
the
storage
ring
uses
RF
gap
voltage
modulation
to
combat
the
longitudinal
upgrade, the storage ring uses RF gap voltage modulation to combat the longitudinal
instability [8]
[8] in
in routine
routine operation.
operation. Figure
Figure 77 shows
instability
shows the
the effect
effect of
of the
the RF
RFthgap
gap voltage
voltage
modulation. The
The figure
figure shows
shows the
the 2fs
2fs upper
upper sideband
modulation.
sideband of
of the
the 200
200th revolution
revolution
harmonics. The
The modulation
modulation amplitude
amplitude is
is kept
kept constant
constant with
harmonics.
with aa 10%
10% gap
gap voltage.
voltage. The
The
frequency
is
scanned
from
47.5
kHz
to
51.5
kHz.
The
sharp
line
spectrum
frequency is scanned from 47.5 kHz to 51.5 kHz. The sharp line spectrum isis the
the
modulated source
source and
and the
the broad
broad spectrum
spectrum is
is due
modulated
due to
to the
the instabilities.
instabilities. When
When the
the
modulation frequency
frequency is
is near
near 2fs
2fs (49.5
(49.5 kHz),
kHz), the
the instability
instability is
modulation
is suppressed.
suppressed. The
The motion
motion
of
the
gap
voltage
modulated
beam
near
2fs
follows
a
dumbbell
like
shape
of the gap voltage modulated beam near 2fs follows a dumbbell like shape rotated
rotated in
in
phase space
space with
with aa frequency
frequency of
of 1fs.
Amplitude modulation
phase
Ifs. Amplitude
modulation is
is introduced
introduced and
and
possibly detect
detect by
by the
the gain
gain measurement
measurement circuitry
circuitry in
in AD8302.
possibly
AD8302. The
The gain
gain measurement
measurement
capability
of
AD8302
enables
it
to
detect
the
amplitude
variation.
Figure
capability of AD8302 enables it to detect the amplitude variation. Figure 88 illustrates
illustrates
the magnitude
magnitude response
response of
of the
the gap
gap voltage
voltage modulation
modulation beam
the
beam transfer
transfer function.
function. The
The
gap voltage
voltage response
response modulation
modulation amplitude
amplitude varies
gap
varies from
from 5%
5% to
to 77 %.
%. Figure
Figure 8(a)
8(a)
shows the
the DSA
DSA output
output frequency
frequency upward
upward sweep
sweep show
shows
show and
and 8(b)
8(b) shows
shows the
the downward
downward
sweep. Strong
Strong hysteresis
hysteresis is
is observed.
observed. The
sweep.
The hysteresis
hysteresis increases
increases with
with the
the excitation
excitation
amplitude. The beam stable region is located the valley near the crest and near 2fs.
amplitude. The beam stable region is located the valley near the crest and near 2fs.
Further study is required to obtain clearly the gap voltage modulation beam transfer
Further
study is required to obtain clearly the gap voltage modulation beam transfer
function.
function.
528
FIGURE
7.
Gap
voltage
modulation spectrums
spectrums as
scan.
FIGURE
modulation frequency
frequency scan.
scan.
FIGURE 7.
7. Gap
Gap voltage
voltage modulation
as aa function
function of
of modulation
modulation
frequency
(8a)
The
frequency
sweep.
(8a) The
The frequency
frequency upward
upward
(8a)
upward sweep.
sweep.
(8b)
The
frequency
sweep.
(8b) The
The frequency
frequency downward
downward
sweep.
(8b)
downward
sweep. voltage modulation.
Amplitude
FIGURE
8.
Amplitude detector
detector responses
responses during
during perform
perform gap
FIGURE
8.
FIGURE 8. Amplitude detector responses during perform gap
gap voltage
voltage modulation.
modulation.
529
SUMMARY
The AD8302 based detector is simple and easy to implement. The detector
combines two functions in one unit. Thus, it doesn't need complex circuitry. The
detection frequency is up to the S band. The detection bandwidth is approximately
30MHz, so amplitude and phase variation can be measured on a time scale of 50 nsec.
The amplitude sensitivity is 30 mV/dB and the phase sensitivity is 10 mV/Degree.
These features of the detector satisfy meet general purpose measurement
requirements.
This simple amplitude and phase detector have several possible applications,
including (1) studying beam transfer functions; (2) monitoring low precision RF
parameters; (3) measuring S-band LINAC RF parameters; (4) acting as a simple
log-ratio processor for BPM applications, working at the RF frequency. This report
implement a simple detector, based upon the AD8302 chip, to measure a beam
transfer function. The performance of the detector module is still being improved to
for use in various applications.
REFERENCE
[1]. D. Cheever, et al., "The Bates Phase and Amplitude Monitor System", ICALEPCS'2001
proceeding, Nov 27-30. San 'Jose.
[2] M. Satoh, et al., "First Beam Test of A O-A Initial Beam Loading Compensation for Electron
Linacs", Proceedings of the 2001 Particle Accelerator Conference, Chicago, p. 3954, 2001.
[3]. AD8302 datasheet, data sheet of Analog Device Incorporation.
[4]. K. Yanagida, et al., "Signal Processor for Spring-8 Linac BPM", DIPAC 2001 Proceedings, ESRF,
Grenoble, May 5-9, 2001.
[5] K. Yanagida et al., " A BPM System for the Spring-8 Linac", Proc. Of the 20th Int. Linac Conf.,
Monterey USA, Aug. 2000, pp 190-192.
[6] J. M. Byrd, et al., "Nonlinear Effects of Phase Modulation in an Electron Storage Ring", Phys. Rev.
E57, 4706 (1998).
[7] J. M. Byrd, "Longitudinal Beam Transfer Function Diagnostics in an Electron Storage Ring",
Particle Accelerator, 1997, Vol. 57, pp. 159-173..
[8] D. Li, et al., "Effects of rf voltage modulation on particle motion", Nucl. Instrum. and Meth., NIM
A364, 205 (1995).
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