Moteur de recherche de fiches techniques de composants électroniques
Selected language     French  ▼
Nom de la pièce
         Description


AD8362-EVAL Datasheet(Fiches technique) 16 Page - Analog Devices

Numéro de pièce AD8362-EVAL
Description  50 Hz to 2.7 GHz 60 dB TruPwr™ Detector
Télécharger  36 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Fabricant  AD [Analog Devices]
Site Internet  http://www.analog.com
Logo 

 16 page
background image
AD8362
Rev. B | Page 16 of 36
Accordingly, VTGT (and its fractional part VATG) determines the
output that must be provided by the VGA for the AGC loop to
settle. Since the scaling parameters of the two squarers are
accurately matched, it follows that Equation 3 is satisfied only
when
()
2
2
ATG
SIG
V
V
MEAN
=
(4)
In a formal solution, one would then extract the square root of
both sides to provide an explicit value for the root-mean-square
(rms) value. However, it is apparent that by forcing this identity,
through varying the VGA gain and extracting the mean value
by the filter provided by the capacitor(s), the system inherently
establishes the relationship
(
)
ATG
SIG
V
V
rms
=
(5)
Substituting the value of VSIG from Equation 2, we have
(
)
[
]
ATG
GNS
IN
O
V
V
VSET
V
G
rms
=
exp
(6)
As a measurement device, VIN is the unknown quantity and all
other parameters can be fixed by design. Solving Equation 6:
[
]
(
)
GNS
ATG
IN
O
V
VSET
V
V
G
rms
exp
=
(7)
so
()
[
]
Z
IN
GNS
V
V
rms
V
VSET
log
=
(8)
The quantity VZ = VATG/GO is defined as the intercept voltage
because VSET must be 0 when rms (VIN) = VZ.
When connected as a measurement device, the output of the
buffer is tied directly to VSET, which closes the AGC loop.
Making the substitution VOUT = VSET and changing the log
base to 10, as needed in a decibel conversion, we have
()
[
]
Z
IN
SLP
V
V
rms
V
VOUT
10
log
=
(9)
where VSLP is the slope voltage, that is, the change in output
voltage for each decade of change in the input amplitude.
(Note that VSLP = VGNS log (10) = 2.303 VGNS). In the AD8362,
VSLP is laser trimmed to 1 V using a 100 MHz test signal.
Because a decade corresponds to 20 dB, this slope may also be
stated as 50 mV/dB. It is later shown how the effective value of
VSLP may be altered by the user.
Likewise, the intercept VZ is also laser trimmed to 316 µV
(−70 dBV). In an ideal system, VOUT would cross zero for an
rms input of that value. In a single-supply realization of the
function, VOUT cannot run fully down to ground; here, VZ is
the extrapolated value. In measurement modes, the output
ranges from 0.5 V for VIN = 1 mV (input values are stated as
rms, outputs values as dc), up to a voltage 60 dB × 50 mV/dB =
3 V above this for VIN = 1 V, that is, to 3.5 V. Figure 43 shows the
ideal form of Equation 9 scaled as in the AD8362.
RMS INPUT VOLTAGE (100
µV TO 3.2V)
0
100
µV
1mV
10mV
100mV
1V
10V
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Figure 43. Ideal Response of the AD8362
EFFECT OF INPUT COUPLING ON THE INTERCEPT
VALUE
Reductions of VIN due to coupling losses directly affect VZ. In
high frequency applications, several factors contribute to the
coupling of the source into the IC, including the board and
package resonances and attenuation. Any uncertainties in the
input impedance result in the intercept expressed in power
terms, which is nominally −57 dBm for a 50 Ω system, being
less accurately determined than when stated in dBV (that is, in
pure voltage) terms. On the other hand, the slope VSLP is
unaffected by all such impedance or coupling uncertainties.
OFFSET ELIMINATION
To address the small dc offsets that arise in the variable gain
amplifier, an offset-nulling loop is used. The high-pass corner
frequency of this loop is internally preset to 1 MHz, sufficiently
low for most HF applications. When using the AD8362 in LF
applications, the corner frequency can be reduced as needed by
the addition of a capacitor from the CHPF pin to ground having
a nominal value of 200 µF/Hz. For example, to lower the high-
pass corner frequency to 150 Hz, a capacitance of 1.33 µF is
required. The offset voltage varies depending on the actual gain
at which the VGA is operating, and thus, on the input signal
amplitude.
Baseline variations of this sort are a common aspect of all
VGAs, although more evident in the AD8362 because of the
method of its implementation, which causes the offsets to
ripple along the gain axis with a period of 6.33 dB. When an
excessively large value of CHPF is used, the offset correction
process may lag the more rapid changes in the VGA’s gain,
which may increase the time required for the loop to fully settle
for a given steady input amplitude.




Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36 


Datasheet Download



Numéro de composants électroniques

Numéro de pièceDescription des composantsHtml ViewFabricant
AD8361LF to 2.5 GHz TruPwr™ Detector 1 2 3 4 5 MoreAnalog Devices
PH2729-8.5MRadar Pulsed Power Transistor 8.5W 100us Pulse 10% Duty 2.7 - 2.9 GHz 1 2 Tyco Electronics
AD83181 MHz - 8 GHz 60 dB Logarithmic Detector/Controller 1 2 3 4 5 MoreAnalog Devices
PH2729-110MRadar Pulsed Power Transistor 110W 100us Pulse 10% Duty 2.7 - 2.9 GHz 1 2 Tyco Electronics
AD8302LF.2.7 GHz RF/IF Gain and Phase Detector 1 2 3 4 5 MoreAnalog Devices
PH2729-130MRadar Pulsed Power Transistor 130W 100us Pulse 10% Duty 2.7 - 2.9 GHz 1 Tyco Electronics
TD7627FN30WIRE AND I2C BUS SYSTEM 2.7 GHz DIRECT TWO MODULUS-TYPE FREQUENCY SYNTHSIZER FOR CATV 1 2 3 4 5 MoreToshiba Semiconductor
MD54-0007Low Cost MMIC Mixer 2.1 - 2.7 GHz 1 2 3 Tyco Electronics
UPC2745T3 V 2.7 GHz Si MMIC WIDEBAND AMPLIFIER 1 2 3 4 5 NEC
ADL550150 MHz to 4 GHz TruPwr Detector 1 2 3 4 5 MoreAnalog Devices

Lien URL

AllDATASHEET vous a-t-il été utile ?   [ DONATE ]  

À propos de Alldatasheet   |   Publicité   |   Contactez-nous   |   Politique de confidentialité   |   Favoris   |   Echange de liens   |   Fabricants
All Rights Reserved © Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  , Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp  |   Russian : Alldatasheetru.com
Korean : Alldatasheet.co.kr   |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com  |   Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl