AD8307ANZ Analog Devices Inc, AD8307ANZ Datasheet - Page 22

• Manufacturer Part Number: AD8307ANZ
• Description: IC LOGARITHMIC AMP 8-DIP
• Manufacturer: Analog Devices Inc
• Type: Logarithmic Amplifierr

Specifications of AD8307ANZ

• Applications: Receiver Signal Strength Indication (RSSI)
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• No. Of Amplifiers: 1
• Dynamic Range, Decades: 4.6
• Scale Factor V / Decade: 0.5
• Response Time: 500ns
• Supply Voltage Range: 2.7V To 5.5V
• Supply Current: 8mA
• Input Offset Voltage: 50µV
• Amplifier Type: Logarithmic
• Bandwidth: 900 MHz
• Current, Input Bias: 10 μA
• Current, Supply: 8 mA
• Package Type: PDIP-8
• Resistance, Input: 1.1 Kilohms
• Temperature, Operating, Range: -40 to +85 °C
• Voltage, Input: 7.5 V
• Voltage, Input Offset: 50 mV
• Voltage, Noise: 1.5 nV/sqrt Hz
• Voltage, Supply: 2.7 to 5.5 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

AD8307
OPERATION AT LOW FREQUENCIES
The AD8307 provides excellent logarithmic conformance at
signal frequencies that can be arbitrarily low, depending only
on the values used for the input coupling capacitors. It can also
be desirable to add a low-pass input filter to desensitize the log
amp to HF signals. Figure 44 shows a simple arrangement, provid-
ing coupling with an attenuation of 20 dB; the intercept is shifted
up by this attenuation, from −84 dBm to −64 dBm, and the
input range is now 0.5 mV to 20 V (sine amplitude).
A high-pass 3 dB corner frequency of nominally 3 Hz is set by
the 10 μF coupling capacitors, C1 and C2, which are preferably
tantalum electrolytics (note the polarity) and a low-pass 3 dB
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
–100
Figure 43. Results for 120 dB Measurement System
–80
WITH FILTER
INPUT LEVEL (dBm)
–60
WITHOUT
FILTER
–40
(WITH FILTER)
ERROR
–20
0
20
2
1
0
–1
–2
Rev. D | Page 22 of 24
corner frequency of 200 kHz (set by C3 and the effective resis-
tance at the input of 1 kΩ). The −1% amplitude error points
occur at 20 Hz and 30 kHz. These are readily altered to suit other
applications by simple scaling. When C3 is zero, the low-pass
corner is at 200 MHz. Note that the lower end of the dynamic
range is improved by this capacitor, which essentially provides
an HF short circuit at the input. This significantly lowers the
wideband noise; the noise reduction is about 2 dB compared to
when the AD8307 is driven from a 50 Ω source. Ensure that the
output is free of postdemodulation ripple by lowering the low-pass
filter time constant, which is provided by C5. With the value shown
in Figure 44, the output time constant is 125 ms.
See Figure 40 for a more elaborate filter. To improve the law
conformance at very low signal levels and at low frequencies, add
C4 to the offset compensation loop.
AMPLITUDE
0.5mV TO
20V SINE
Figure 44. Connections for Low Frequency Operation
V
IN
NC = NO CONNECT
10µF
C2
10µF
C1
+
+
750pF
5kΩ
5kΩ
R2
R1
C3
0.1µF
INM COM OFS OUT
INP VPS ENB INT
8
1
AD8307
5V
1µF
7
2
C4
4.7Ω
6
3
NC
5
4
C5
1µF
V
25mV/dB
OUT