AD8318ACPZ-REEL7 Analog Devices Inc, AD8318ACPZ-REEL7 Datasheet - Page 11

• Manufacturer Part Number: AD8318ACPZ-REEL7
• Description: IC, LOGARITHMIC AMP, 12NS, LFCSP-16
• Manufacturer: Analog Devices Inc

Specifications of AD8318ACPZ-REEL7

• No. Of Amplifiers: 1
• Dynamic Range, Decades: 70
• Response Time: 12ns
• Supply Voltage Range: 4.5V To 5.5V
• Amplifier Case Style: LFCSP
• No. Of Pins: 16
• Supply Current: 68mA
• Design Resources: Stable, Closed-Loop Automatic Power Control for RF Appls (CN0050) Software Calibrated, 1 MHz to 8 GHz, 70 dB RF Power Measurement System Using AD8318 (CN0150)
• Frequency: 1MHz ~ 8GHz
• Rf Type: RADAR, 802.11/Wi-Fi, 8.2.16/WiMax, Wireless LAN
• Input Range: -60dBm ~ -2dBm
• Accuracy: ±1dB
• Voltage - Supply: 4.5 V ~ 5.5 V
• Current - Supply: 68mA
• Package / Case: 16-VQFN, CSP Exposed Pad
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: AD8318ACPZ-REEL7; AD8318ACPZ-REEL7TR

THEORY OF OPERATION
The AD8318 is a 9-stage demodulating logarithmic amplifier
that provides RF measurement and power amplifier control
functions. The design of the AD8318 is similar to the
logarithmic detector/controller. However, the AD8318 input
frequency range extends to 8 GHz with a 60 dB dynamic range.
Other improvements include: reduced intercept variability vs.
temperature, increased dynamic range at higher frequencies,
low noise measurement and controller output (VOUT),
adjustable low-pass corner frequency (CLPF), temperature
sensor output (TEMP), negative transfer function slope for
higher accuracy, and 10 ns response time for RF burst detection
capability. A block diagram is shown in Figure 22.
A fully differential design, using a proprietary high speed SiGe
process, extends high frequency performance. Input INHI
receives the signal with a low frequency impedance of nominally
1200 Ω in parallel with 0.7 pF. The maximum input with ±1 dB
log conformance error is typically 0 dBm (re: 50 Ω). The noise
spectral density referred to the input is 1.15 nV/√Hz, which is
equivalent to a voltage of 118 μV rms in a 10.5 GHz bandwidth,
or a noise power of −66 dBm (re: 50 Ω). This noise spectral
density sets the lower limit of the dynamic range. However, the
low end accuracy of the AD8318 is enhanced by specially
shaping the demodulating transfer characteristic to partially
compensate for errors due to internal noise.
TEMP
INLO
INHI
DET
VPSI
SENSOR
TEMP
CMIP
DET
Figure 22. Block Diagram
ENBL
GAIN
BIAS
DET
SLOPE
DET
TADJ
VPSO
CMOP
I
I
V
V
AD8313
VSET
VOUT
CLPF
Rev. B | Page 11 of 24
CMIP, the input system common pin, provides a quality low
impedance connection to the printed circuit board (PCB)
ground via four package pins. Ground the package paddle,
which is internally connected to the CMIP pin, to the PCB to
reduce thermal impedance from the die to the PCB.
The logarithmic function is approximated in a piecewise
fashion by nine cascaded gain stages. For a more complete
explanation of the logarithm approximation, refer to the
AD8307
8.7 dB each and a 3 dB bandwidth of 10.5 GHz.
Using precision biasing, the gain is stabilized over temperature
and supply variations. Because the cascaded gain stages are
dc-coupled, the overall dc gain is high. An offset compensation
loop is included to correct for offsets within the cascaded cells.
At the output of each of the gain stages, a square-law detector
cell rectifies the signal. The RF signal voltages are converted to a
fluctuating differential current with an average value that
increases with signal level. Along with the nine gain stages and
detector cells, an additional detector is included at the input of
the AD8318, altogether providing a 60 dB dynamic range. After
the detector currents are summed and filtered, the function
is formed at the summing node,
where:
I
V
V
the output voltage would be 0 V if capable of going to 0 V).
D
IN
INTERCEPT
is the internally set detector current.
is the input signal voltage.
I
D
× log
data sheet. The cells have a nominal voltage gain of
is the intercept voltage (that is, when V
10
(V
IN
/V
INTERCEPT
)
IN
= V
AD8318
INTERCEPT
(1)
,