ADL5902-EVALZ AD [Analog Devices], ADL5902-EVALZ Datasheet - Page 15

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

THEORY OF OPERATION
The ADL5902 is a 50 MHz to 9 GHz true rms responding
detector with a 65 dB measurement range at 2.14 GHz and a
greater than 56 dB measurement range at frequencies up to
6 GHz. It incorporates a modified
increases the frequency range and improves measurement
accuracy at high frequencies. Transfer function peak-to-peak
ripple has been reduced to <±0.1 dB over the entire dynamic
range. Temperature stability of the rms output measurements
provides <±0.3 dB error, typically, over the specified temperature
range of −40°C to 125°C through proprietary techniques. The
device accurately measures waveforms that have a high peak-to-
rms ratio (crest factor).
The ADL5902 consists of a high performance AGC loop. As
shown in Figure 36, the AGC loop comprises a wide bandwidth
variable gain amplifier (VGA), square law detectors, an amplitude
target circuit, and an output driver. For a more detailed description
of the functional blocks, see the AD8362 data sheet.
The nomenclature used in this data sheet to distinguish
between a pin name and the signal on that pin is as follows:
•
•
SQUARE LAW DETECTOR AND AMPLITUDE TARGET
The VGA gain has the form
where:
G
O
is the basic fixed gain.
The pin name is all uppercase, for example, VPOS,
COMM, and VOUT.
The signal name or a value associated with that pin is the
pin mnemonic with a partial subscript, for example, C
and V
G
SET
= G
OUT
O
.
e
−
(
V
SET
/
V
GNS
)
VSET
INLO
INHI
AD8362
G
SET
architecture that
VPOS
VGA
C
(INTERNAL)
H
V
SIG
Figure 36. Simplified Architecture Details
X
2
LPF
I
SQR
SUMMING
Rev. 0 | Page 15 of 28
(1)
NODE
C
(EXTERNAL)
I
TGT
LPF
TEMPERATURE COMPENSATION
TEMPERATURE
REFERENCE
X
BAND GAP
2
SENSOR
V
ATG
V
change per voltage). The gain decreases with increasing V
The VGA output is
where RF
ADL5902.
The output of the VGA, V
law detector. The detector provides the true rms response of the
RF input signal, independent of waveform. The detector output,
I
difference between I
I
external capacitor attached to the CLPF pin at the summing
node. C
external capacitance connected to the CLPF pin, can be used to
arbitrarily increase the averaging time while trading off with the
response time. When the AGC loop is at equilibrium
This equilibrium occurs only when
where V
can conveniently be connected to the VREF pin through a voltage
divider to establish a target rms voltage, V
V
Because the square law detectors are electrically identical and
well matched, process and temperature dependent variations
are effectively cancelled.
SQR
TGT
GNS
TGT
AND BIAS
=
, is a fluctuating current with positive mean value. The
C
(INTERNAL)
, is integrated by the parallel combination of C
V
F
V
Mean(I
Mean(V
is a scaling voltage that defines the gain slope (the decibel
= 0.8 V.
20
TGT
SIG
F
TGT
= G
is an on-chip 26 pF filter capacitor, and C
IN
is the ac voltage applied to the input terminals of the
is the voltage presented at the VTGT pin. This pin
SQR
SET
SIG
) = I
2
× RF
) = V
TGT
SQR
IN
TGT
= G
and an internally generated current,
2
VTGT
CLPF
VOUT
COMM
TADJ/PWDN
TEMP (1.4V)
VREF (2.3V)
SIG
O
× RF
, is applied to a wideband square
IN
e
−
(
V
ATG
SET
/
, of ~40 mV rms when
V
GNS
)
F
ADL5902
LPF
and the
, the
SET
.
(2)
(3)
(4)