AD8313ARM Analog Devices Inc, AD8313ARM Datasheet - Page 20

• Manufacturer Part Number: AD8313ARM
• Description: IC LOGARTIHMIC AMP 70DB 8-MSOP
• Manufacturer: Analog Devices Inc
• Type: Logarithmic Ampr

Specifications of AD8313ARM

• Rohs Status: RoHS non-compliant
• Frequency: 100MHz ~ 2.5GHz
• Rf Type: RADAR, 802.11/Wi-Fi, 8.2.16/WiMax, Wireless LAN
• Input Range: -65dBm ~ 0dBm
• Accuracy: ±1dB
• Voltage - Supply: 2.7 V ~ 5.5 V
• Current - Supply: 13.7mA
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Number Of Channels: 1
• Number Of Elements: 8
• Power Supply Requirement: Single
• Voltage Gain Db: 84dB
• Input Resistance: 0.0009@5VMohm
• Input Bias Current: 10@5VnA
• Single Supply Voltage (typ): 3/5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Dissipation: 200mW
• Rail/rail I/o Type: Rail to Rail Output
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 8
• Package Type: MSOP
• Lead Free Status / RoHS Status: Not Compliant

AD8313
EVALUATION BOARD
SCHEMATIC AND LAYOUT
Figure 44 shows the schematic of the AD8313 evaluation board.
Note that uninstalled components are indicated as open. This
board contains the AD8313 as well as the AD8009 current-
feedback operational amplifier.
This is a 4-layer board (top and bottom signal layers, ground,
and power). The top layer silkscreen and layout are shown in
Figure 42 and Figure 43. A detailed drawing of the recommended
PCB footprint for the MSOP package and the pads for the
matching components are shown in Figure 45.
The vacant portions of the signal and power layers are filled out
with ground plane for general noise suppression. To ensure a low
impedance connection between the planes, there are multiple
through-hole connections to the RF ground plane. While the
ground planes on the power and signal planes are used as
general-purpose ground returns, any RF grounds related to the
input matching network (for example, C2) are returned directly
to the RF internal ground plane.
GENERAL OPERATION
The AD8313 should be powered by a single supply in the range
of 2.7 V to 5.5 V. The power supply to each AD8313 VPOS pin is
decoupled by a 10 Ω resistor and a 0.1 µF capacitor. The AD8009
can run on either single or dual supplies, +5 V to ±6 V. Both the
positive and negative supply traces are decoupled using a 0.1 µF
capacitor. Pads are provided for a series resistor or inductor to
provide additional supply filtering.
The two signal inputs are ac-coupled using 680 pF high quality
RF capacitors (C1, C2). A 53.6 Ω resistor across the differential
signal inputs (INHI, INLO) combines with the internal 900 Ω
input impedance to give a broadband input impedance of 50.6 Ω.
This termination is not optimal from a noise perspective due to
the Johnson noise of the 53.6 Ω resistor. Neither does it account
for the AD8313’s reactive input impedance nor for the decrease
over frequency of the resistive component of the input imped-
ance. However, it does allow evaluation of the AD8313 over its
complete frequency range without having to design multiple
matching networks.
For optimum performance, a narrow-band match can be
implemented by replacing the 53.6 Ω resistor (labeled L/R) with
an RF inductor and replacing the 680 pF capacitors with
appropriate values. The Narrow-Band LC Matching Example
at 100 MHz section includes a table of recommended values for
selected frequencies and explains the method of calculation.
Switch 1 is used to select between power-up and power-down
modes. Connecting the PWDN pin to ground enables normal
operation of the AD8313. In the opposite position, the PWDN
pin can be driven externally (SMA connector labeled ENBL) to
either device state, or it can be allowed to float to a disabled
device state.
Rev. D | Page 20 of 24
The evaluation board comes with the AD8313 configured to
operate in RSSI/measurement mode. This mode is set by the
0 Ω resistor (R11), which shorts the VOUT and VSET pins to
each other. When using the AD8009, the AD8313 logarithmic
output appears on the SMA connector labeled VOUT. Using
only the AD8313, the log output can be measured at TP1 or the
SMA connector labeled VSET.
USING THE AD8009 OPERATIONAL AMPLIFIER
The AD8313 can supply only 400 µA at VOUT. It is also sensitive
to capacitive loading, which can cause inaccurate measurements,
especially in applications where the AD8313 is used to measure
the envelope of RF bursts.
The AD8009 alleviates both of these issues. It is an ultrahigh
speed current feedback amplifier capable of delivering over
175 mA of load current, with a slew rate of 5,500 V/µs, which
results in a rise time of 545 ps, making it ideal as a pulse amplifier.
The AD8009 is configured as a buffer amplifier with a gain of 1.
Other gain options can be implemented by installing the appro-
priate resistors at R10 and R12.
Various output filtering and loading options are available using
R5, R6, and C6. Note that some capacitive loads may cause the
AD8009 to become unstable. It is recommended that a 42.2 Ω
resistor be installed at R5 when driving a capacitive load. More
details can be found in the AD8009 data sheet.
VARYING THE LOGARITHMIC SLOPE
The slope of the AD8313 can be increased from its nominal
value of 18 mV/dB to a maximum of 40 mV/dB by removing
R11, the 0 Ω resistor, which shorts VSET to VOUT. VSET and
VOUT are now connected through the 20 kΩ potentiometer.
The AD8009 must be configured for a gain of 1 to accurately
vary the slope of the AD8313.
OPERATING IN CONTROLLER MODE
To put the AD8313 into controller mode, R7 and R11 should
be removed, breaking the link between VOUT and VSET. The
VSET pin can then be driven externally via the SMA connector
labeled VSET.
RF BURST RESPONSE
The VOUT pin of the AD8313 is very sensitive to capacitive
loading, as a result care must be taken when measuring the
device’s response to RF bursts. For best possible response time
measurements it is recommended that the AD8009 be used to
buffer the output from the AD8313. No connection should be
made to TP1, the added load will effect the response time.