AD8330 Analog Devices, AD8330 Datasheet - Page 24

• Manufacturer Part Number: AD8330
• Description: Low Cost DC-150MHz Variable Gain Amplifier
• Manufacturer: Analog Devices

AD8330
The upper panel in Figure 23 shows time-domain output for 14
3 dB steps in input amplitude from 5.4 mV to 1.7 V. The wave-
forms in Figure 22 show the AGC voltage V
This simple detector exhibits a temperature variation in the
differential output amplitude of about 4 mV/ C. It provides a
fast attack time (an increase in the input is quickly leveled to the
nominal output, due to the high peak currents in Q1) and a slow
release time (a decrease in the input is not restored as quickly).
The voltage at the VDBS pin may be used as an RSSI output,
scaled 30 mV/dB. Note that the attack time can be halved by adding
a second transistor as shown in the box (Figure 21). For operation
at lower frequencies, the AGC hold capacitor must be increased.
Figure 22. AGC Output vs. Input Amplitude (Simulation)
1.0
0.9
0.8
0.7
0.6
0.5
–50
–40
INPUT
0.1 F
INPUT TO AD8330 – dBV
–30
3.3
VPS1
INHI
INLO
MODE
ENBL
VDBS
Figure 24. Wide Range True RMS Voltmeter (Preliminary)
–20
CMGN
OFST
AD8330
COMM
0.1 F
VPOS
DBS
–10
.
VMAG
0.1 F
CNTR
3.6V
CMOP
VPSO
OPLO
OPHI
3.3
0
0.1 F
C
18nF
FLT
10 F
5V
–24–
3.6V
1
2
3
4
5
6
7
8
Wide Range True RMS Voltmeter
The AD8362 is an rms-responding detector providing a dynamic
range of 60 dB from low frequencies to 2.7 GHz. This may be
increased to 110 dB using an AD8330 as a preconditioner, pro-
vided the noise bandwidth is limited by an interstage low-pass or
band-pass filter.
The VGA also provides an input port that is easier to drive
than the 200
general scheme.
Both the AD8330 and AD8362 provide linear-in-decibel control
interfaces. Thus when the output of the latter is used to control
the gain of the former, this functional form is unaffected. The
overall scaling is 33 mV/dB. Figure 25 shows the time domain
response using a loop filter capacitor of 10 nF, for inputs ranging
from 10 V to 1 V rms, that is, a 100 dB measurement range.
COMM
CHPF
DECL
INHI
INLO
DECL
PWDN
COMM
AD8362
Figure 23. Time Domain Waveforms (Simulation)
(See Text)
1.00
1.75
1.50
1.25
0.75
0.50
0.25
–1
–2
–3
–4
0
3
2
1
0
0
ACOM
ACOM
VPOS
VOUT
VREF
VTGT
VSET
CLPF
10
V
input of the AD8362. Figure 24 shows the
DBS
16
15
14
13
12
11
10
20
9
30
40
3.3
10 F
50
0.1 F
60
TIME – s
70
6.04k
4.02k
80
VOUT
90 100 110 120 130 140 150
OUTPUT
REV. A