ADL5902-EVALZ AD [Analog Devices], ADL5902-EVALZ Datasheet - Page 16

• Manufacturer Part Number: ADL5902-EVALZ
• Description: 50 MHz to 9 GHz 65 dB TruPwr Detector
• Manufacturer: AD [Analog Devices]

ADL5902
When forcing the previous identity by varying the VGA setpoint, it
is apparent that
Substituting the value of V
When connected as a measurement device, V
for V
where:
V
V
When RMS(RF
log
0 V if the ADL5902 had no sensitivity limit. The P
decibels relative to 1 milliwatt, that is, dBm) corresponding to
Vz (in volts) in ADL5902 is given by the following equation:
where V
P
milliwatt, given by the following expression:
where dBm(V
1 milliwatt corresponding to a given V
Combining Equation 8 and Equation 9 results in
For the ADL5902, V
given by V
then decreases at higher frequencies. V
and
At 2.14 GHz, V
This results in a P
the value in Table 1 due to the choice of calibration points and
the slight nonideality of the response.
In most applications, the AGC loop is closed through the
setpoint interface and the VSET pin. In measurement mode,
VOUT is directly connected to VSET (see the Measurement
Mode Basic Connections section for more information). In
controller mode, a control voltage is applied to VSET, and the
VOUT pin typically drives the control input of an amplification
or attenuation system. In this case, the voltage at the VSET pin
forces a signal amplitude at the RF inputs of the ADL5902 that
balances the system through feedback.
RF INPUT INTERFACE
Figure 37 shows the RF input connections within the ADL5902.
The input impedance is set primarily by an internal 2 kΩ resistor
connected between INHI and INLO. A dc level of approximately
MINDET
SLOPE
Z
is the intercept voltage.
10
(1) = 0. This makes the intercept the input that forces V
RMS(V
RMS(G
V
P
P
P
V
dBm (V
OUT
INTERCEPT
MINDET
INTERCEPT
OUT
is 1.06 V/decade (or 53 mV/dB) at 2.14 GHz.
ATG
is the minimum detectable signal in decibels relative to 1
PEDISTAL
as a function of RF
= 40 mV
= V
TGT
= dBm (V
SIG
0
ATG
× RF
/20. G
SLOPE
ATG
= −(V
= −(V
) = √(Mean(V
is the VSET interface’s pedestal voltage, and
SLOPE
IN
) = 10
) is the equivalent power in decibels relative to
) = V
INTERCEPT
IN
× log
O
≈ 53 mV/dB and G
PEDISTAL
PEDISTAL
e
PEDISTAL
is 45 dB below approximately 4 GHz and
ATG
log
Z

, this implies that V
10
(
V
) – G
10
(RMS(RF
SET
((
≈ −65 dBm. This differs slightly from
SIG
/V
/V
is approximately 0.275 V and V
IN
/
40
SIG
V
,
SLOPE
SLOPE
from Equation 2 results in
GNS
O
2
mV)
)) = √(V
)
) = V
) + P
) + dBm (V
IN
2
)/V
/50 Ω)/1 mW) ≈ −14.9 dBm
ATG
MINDET
TGT
TGT
Z
O
ATG
)
at 2.14 GHz = 45 dB.
.
2
= 0.8 V; therefore,
OUT
) = V
ATG
SET
= 0 V because
) – G
INTERCEPT
= V
ATG
OUT
O
. Solving
(in
OUT
ATG
(10)
Rev. 0 | Page 16 of 28
=
(5)
(6)
(7)
(8)
(9)
is
half the supply voltage on each pin is established internally.
Either the INHI or INLO pin can be used as the single-ended
RF input pin. Signal coupling capacitors must be connected
from the input signal to the INHI and INLO pins. A single
external 60.4 Ω resistor to ground from the desired input
creates an equivalent 50 Ω impedance over a broad section of
the operating frequency range. The other input pin should be
RF ac-coupled to common (ground). The input signal high-pass
corner formed by the input coupling capacitor’s internal and
external resistances is
where C is the capacitance in farads and f
input coupling capacitors must be large enough in value to pass
the input signal frequency of interest and determine the low end
of the frequency response. INHI and INLO can also be driven
differentially using a balun.
INHI
Extensive ESD protection is employed on the RF inputs, and
this protection limits the maximum possible input to the
ADL5902.
SMALL SIGNAL LOOP RESPONSE
The ADL5902 uses a VGA in a loop to force a squared RF signal
to be equal to a squared dc voltage. This nonlinear loop can be
simplified and solved for a small signal loop response. The low-
pass corner pole is given by
where:
I
C
Freq
I
V
g
typically recommended 0.8 V, I
value of this current varies with temperature; therefore, the
small signal pole varies with temperature. However, because the
RF squaring circuit and dc squaring circuit track with temperature,
COMM
VPOS
TGT
TGT
m
LPF
TGT
is approximately 18.9 μs; therefore, with V
is in amperes.
is in farads.
is derived from V
LP
f
Freq
I
multiplied by a transresistance, namely
HIGHPASS
TGT
is in hertz.
ESD
ESD
ESD
= g
LP
≈ 1.83 × I
m
= 1/(2 × π × 50 × C)
× V
ESD
ESD
TGT
2kΩ
2
TGT
TGT
ESD
ESD
/(C
VBIAS
Figure 37. RF Inputs
; however, I
LPF
LOAD
)
TGT
is approximately 12 μA. The
TGT
ESD
ESD
is a squared value of
2kΩ
HIGHPASS
ESD
ESD
TGT
is in hertz. The
equal to the
ESD
ESD
INLO
(11)
(12)
(13)