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ADL5513 参数 Datasheet PDF下载

ADL5513图片预览
型号: ADL5513
PDF下载: 下载PDF文件 查看货源
内容描述: 利用AD8368可变增益放大器扩展ADL5513对数检测器的动态范围 [Extending the Dynamic Range of the ADL5513 Logarithmic Detector Using the AD8368 Variable Gain Amplifier]
分类和应用: 放大器
文件页数/大小: 3 页 / 123 K
品牌: AD [ ANALOG DEVICES ]
 浏览型号ADL5513的Datasheet PDF文件第1页浏览型号ADL5513的Datasheet PDF文件第3页  
CN-0072
CIRCUIT DESCRIPTION
The ADL5513 logarithmic detector dynamic range can be
extended by adding a separate VGA whose gain control input is
derived directly from V
OUT
. This extends the dynamic range by
the gain control range of the VGA. For the overall measurement
to remain linear in dB, the VGA must provide a linear-in-dB
(exponential) gain control function. The VGA gain must
decrease with an increase in its gain bias in the same way as the
ADL5513. Alternatively, an inverting op amp with suitable level
shifting can be used. It is convenient to select a VGA that needs
only a single 5.0 V supply and is capable of generating a single-
ended output. All of these conditions are met by the AD8368.
mode (MODE pin low) of the AD8368, its gain decreases on a
slope of 37.5 mV/dB to a minimum value of −12 dB for a gain
voltage (VGAIN) of 1.0 V. The voltage, VGAIN, required by the
AD8368 is 50% of the output of the ADL5513. To scale this
voltage, it is necessary to insert a voltage divider at the output of
the ADL5513. Over the 1.5 V range from the output of the
ADL5513, the gain of the AD8368 varies by (0.5 × 1.5 V)÷
(37.5 mV/dB), or 20 dB. Combined with the 75 dB gain span (at
120 MHz) of the ADL5513, this results in a 1.5 V change in
V
OUT
for a 95 dB change at the input to the AD8368.
Due to the amplification of out-of-band noise by the AD8368, a
band-pass filter is used between the AD8368 and ADL5513 to
increase the low-signal sensitivity. The VGA amplifies low
power signals and attenuates high power signals to fit them in
the detectable range of the ADL5513. If an amplifier with higher
gain and lower noise figure is used, better than 90 dB sensitivity
can be achieved for use in a receive-signal-strength-indicator
(RSSI) application.
at 120 MHz and the corresponding error in V
OUT
.
Due to the high frequencies and wide dynamic ranges involved,
the circuit must be constructed on a multilayer PC board that
has at least one layer for the ground plane. Each IC power pin
must be decoupled with a 0.1 µF low inductance ceramic
capacitor as shown in Figure 1. Some power pins have an
additional smaller value decoupling capacitor (low ESL) for
extremely high frequencies. The “0 Ω” resistors on the
schematic represent optional small resistor values (less than
10 Ω) or ferrite beads that may be added for more decoupling.
The data sheets for the ADL5513 and the AD8368 show the
optimal layouts of the respective evaluation boards.
On the underside of both the ADL5513 and the AD8368 chip
scale package there is an exposed paddle. This paddle is
internally connected to the ground of the chip. Solder the
paddle to the low impedance ground plane on the PCB to
ensure specified electrical performance and to provide thermal
relief. It is also recommended that the ground planes on all
layers under the paddle be stitched together with vias to reduce
thermal impedance.
1.750
1.625
1.500
1.375
1.250
Circuit Note
3.0
2.5
2.0
1.5
1.0
0.5
0
–0.5
V
OUT
+25°C
V
OUT
–40°C
V
OUT
+85°C
ERROR +25°C
ERROR –40°C
ERROR +85°C
–80
–70
–60
–50
–40 –30 –20
P
IN
(dBm)
–10
0
10
–1.0
–1.5
–2.0
–2.5
08175-002
V
OUT
(V)
1.125
1.000
0.875
0.750
0.625
0.500
0.375
0.250
–90
–3.0
20
Figure 2. Output and Conformance for the AD8368/ADL5513 Extended
Dynamic Range Circuit at 120 MHz
COMMON VARIATIONS
The application circuit described here can be modified for any
IF frequency within the operating range of the AD8368 and
ADL5513 by selecting the appropriate band-pass filter. For
operation above 800 MHz, the
can be used in place of
the AD8368. The ADL5330 VGA can be used at frequencies
between 10 MHz and 3 GHz. Using the ADL5330 also requires
an inverter between the ADL5330 gain pin and the gain control
voltage from the ADL5513. A single-supply operational
amplifier such as the
can be configured for use as an
inverter in this application.
LEARN MORE
Data Sheets
REVISION HISTORY
7/09—Revision 0: Initial Version
Rev. 0 | Page 2 of 3
ERROR (dB)