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AD606JRZ

P1-P3P4-P6P7-P9P10-P12P13-P13
AD606
REV. B
–9–
Low Frequency Applications
With reasonably sized input coupling capacitors and an optional
input low-pass filter, the AD606 can operate to frequencies as
low as 200 Hz with good log conformance. Figure 8 shows the
schematic, with the low-pass filter included in the dashed box.
This circuit should be built inside a die cast box and the signal
brought in through a coaxial connector. The circuit must also
have a low-pass filter to reject the attenuated RF signals that
would otherwise be rectified along with the desired signal and
be added to the log output. The shielded and filtered circuit has
a 90 dB dynamic range, as shown in Figure 9.
In this circuit, R4 and R5 form a 20 dB attenuator that extends
the input range to 10 V rms. R3 isolates loads from VLOG.
Capacitors C1 and C2 (4.7 µF each), R1, R2, and the AD606’s
input resistance of 2.5 kΩ form a 100 Hz high-pass filter that is
before the AD606; the corner frequency of this filter must be
well below the lowest frequency of interest. In addition, the
offset-correction loop introduces another pole at low signal
levels that is transformed into another high-pass filter because it
is in a feedback path. This indicates that there has to be a
gradual transition from a 40 dB roll off at low signal levels to a
20 dB roll off at high signal levels, at which point the feedback
low pass filter is effectively disabled since the incoming signal
swamps the feedback signal.
This low-pass filter introduces some attenuation due to R1 and
R2 in conjunction with the 2.5 kΩ input resistance of the
AD606. To minimize this effect, the value of R1 and R2 should
be kept as small as possible–100 Ω is a good value since it bal-
ances the need to reduce the attenuation as mentioned above
with the requirement for R1 and R2 to be much larger then the
impedance of C1 and C2 at the low-pass corner frequency, in
our case about 1 MHz.
4
–80 40
3
1
–60
2
020–20–40
INPUT SIGNAL – dBm
V
LOG
– Volts DC
0
100Hz
3.5V
1kHz – 10MHz
90dB
Figure 9. Performance of Low Frequency Circuit at 100 Hz
and 1 kHz to 10 MHz (Note Attenuation)
C1
4.7mF
TO
DVM
R3
1kV
+5V
INHI
COMM
PRUP
VPOS
FIL1
FIL2
LADJ
LMHI
INLO
COMM
ISUM
ILOG
BFIN
VLOG
OPCM
LMLO
AD606JN
NC
0.1mF
NC
C4
4.7mF
NC
R1
100V
LOW-PASS
FILTER
R2
100V
C3
680pF
R4
453V
20dB
ATTENUATOR
R5
51.1V
AC
INPUT
C2
4.7mF
+
+
DIECAST BOX
NC = NO CONNECT
Figure 8. Circuit for Low Frequency Measurements
REV. B
–10–
AD606–Typical Performance Characteristics
5
–25
20
–10
–20
–60
–15
–80
0
–5
0
–20–40
INPUT LEVEL – dBm
NORMALIZED PHASE SHIFT – Degrees
10.7MHz
45MHz
70MHz
Figure 11. Normalized Limiter
Phase Response vs. Input Level at
10.7 MHz, 45 MHz, and 70 MHz
10
–2
–4
–60
–3
–80
1
–1
0
2
3
4
0–40
–20
INPUT AMPLITUDE – dBm
LOGARITHMIC ERROR – dB
T
A
= –258C
T
A
= +708C
T
A
= +258C
Figure 14. Logarithmic Conform-
ance as a Function of Input Level at
10.7 MHz at –25
°
C, +25
°
C, and
+70
°
C
Figure 17. V
LOG
Response to a
10.7 MHz CW Signal Modulated by
a 25
µ
s Wide Pulse with a 25 kHz
Repetition Rate Using 200 pF Input
Coupling Capacitors. The Input Sig-
nal Goes from +5 dBm to –75 dBm
in 20 dB Steps.
0.5
–5.5
20
–2.5
–4.5
–60
–3.5
–80
–0.5
–1.5
0
–20–40
INPUT LEVEL – dBm
NORMALIZED LIMITER OUTPUT – dB
–6.5
–50–70 –10–30
10.7MHz
45MHz
70MHz
Figure 10. Normalized Limiter
Amplitude Response vs. Input Level
at 10.7 MHz, 45 MHz and 70 MHz
4.5
0
10
1
0.5
–60–80
2
1.5
2.5
3
3.5
4
0–20–40
INPUT POWER – dBm
V
LOG
– Volts DC
V
S
= 5.5V
V
S
= 5V
V
S
= 4.5V
T
A
= +258C
Figure 13. V
LOG
Plotted vs. Input
Level at 10.7 MHz as a Function of
Power Supply Voltage
Figure 16. Limiter Response at
Onset of 10.7 MHz Modulated Pulse
at –75 dBm Using 200 pF Input
Coupling Capacitors
PRUP VOLTAGE – Volts
POWER SUPPLY CURRENT – mA
14
0
5
6
2
0.5
4
0
12
8
10
4.543.532.521.51
Figure 12. Supply Current vs. PRUP
Voltage at +25
°
C
5
–5
10
–2
–4
–60
–3
–80
1
–1
0
2
3
4
0–40 –20
INPUT AMPLITUDE – dBm
LOGARITHMIC ERROR – dB
T
A
= –258C
T
A
= +708C
T
A
= +258C
Figure 15. Logarithmic Conform-
ance as a Function of Input Level at
45 MHz at –25
°
C, +25
°
C, and +70
°
C
Figure 18. Limiter Response at
Onset of 70 MHz Modulated Pulse
at –55 dBm Using 200 pF Input
Coupling Capacitors
8/30/99 9 AM
AD606
REV. B
–11–
51.1V
C1
100pF
RF
INPUT
NC
200V
+5V
INHI
COMM
PRUP
VPOS
FIL1
FIL2
LADJ
LMHI
INLO
COMM
ISUM
ILOG
BFIN
VLOG
OPCM
LMLO
AD606JN
NC
C3
150pF
C2
100pF
NC
+5V
NC = NO CONNECT
200V
0.1mF
AD602
–10dB TO +30dB
(10.7MHz SWEPT
GAIN TESTS ONLY)
SWEPT GAIN
TESTS
HEWLETT PACKARD
8112A PULSE
GENERATOR
MODULATED
PULSE
TESTS
FLUKE 6082A
SYNTHESIZED
SIGNAL
GENERATOR
TEKTRONIX 7704A
MAINFRAME
OSCILLOSCOPE
10 x
ATTN
P6201
PROBES
7A18
AMP
6137
PROBES
7A24
AMP
7B53A
TIME-BASE
Figure 22. Test Setup for Characterization Data
Figure 19. V
LOG
Output for a Pulsed
10.7 MHz Input; Top Trace: –35 dBm
to +5 dBm; Middle Trace: –15 dBm to
–55 dBm; Bottom Trace: –35 dBm to –
75 dBm
Figure 20. Example of Test Signal
Used for Figure 19
Figure 21. V
LOG
Output for 10.7 MHz
CW Input with PRUP Toggled ON
and OFF; Top Trace: +5 dBm Input;
Middle Trace: –35 dBm Input; Bottom
Trace: –75 dBm; PRUP Input from
HP8112A: 0 to 4 V, 10
µ
s Pulsewidth
with 10 kHz Repetition Rate
P1-P3P4-P6P7-P9P10-P12P13-P13

AD606JRZ

Mfr. #:
Buy AD606JRZ
Manufacturer:
Analog Devices Inc.
Description:
Logarithmic Amplifiers 50 MHz 80dB DEMODULATING AMP
Lifecycle:
New from this manufacturer.
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