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| 型號(hào)： | AD8307AR-REEL7 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 運(yùn)動(dòng)控制電子 |
| 英文描述： | Low Cost DC-500 MHz, 92 dB Logarithmic Amplifier |
| 中文描述： | LOG OR ANTILOG AMPLIFIER, 490 MHz BAND WIDTH, PDSO8 |
| 封裝： | MS-012AA, SOIC-8 |
| 文件頁(yè)數(shù)： | 15/20頁(yè) |
| 文件大小： | 394K |
| 代理商： | AD8307AR-REEL7 |
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AD8307
–15–
REV. A
APPLIC AT IONS
T he AD8307 is a highly versatile and easily applied log amp
requiring very few external components. Most applications of
this product can be accommodated using the simple connec-
tions shown in the preceding section. A few examples of more
specialized applications are provided here.
Buffered Output
T he output may be buffered, and the slope optionally increased,
using an op amp. If the single-supply capability is to be pre-
served, a suitable component is the AD8031. Like the AD8307,
it is capable of operating from a 2.7 V supply and features a rail-
to-rail output capability; it is available in a 5-pin version and in
dual form as the 8-pin AD8032. Figure 36 shows how the slope
may be increased to 50 mV/dB (1 V per decade), requiring a 5 V
supply (90 dB times 50 mV is a 4.5 V swing). VR1 provides a
±
10% slope adjustment; VR2 provides a
±
3 dB intercept range.
With R2 = 4.99 k
, the slope is adjustable to 25 mV/dB, allow-
ing the use of a 2.7 V supply. Setting R2 to 80.6 k
, it is raised
to 100 mV/dB, providing direct reading in decibels on a digital
voltmeter. Since a 90 dB range now corresponds to a 9 V swing,
a supply of at least this amount is needed for the op amp.
INP VPS ENB INT
AD8307
INM COM OFS OUT
INPUT
–75dBm TO
+16dBm
R
S
C1
4.7
V
6
3dB
NC
0.1
m
F
V
P
, 2.7V – 5.5V
20mV/dB
VR2
50k
V
32.4k
V
VR1
50k
V
AD8031
R1
20k
V
R2
30.1k
V
OUTPUT
50mV/dB
6
10%
COM
FOR V
P
= 3V, R
S
= 20k
V
V
P
= 5V, R
S
= 51k
V
NC = NO CONNECT
Figure 36. Log Amp with Buffered Output
C1 is optional; it lowers the corner frequency of the low-pass
output filter. A value of 0.1
μ
F should be used for applications
in which the output is measured on a voltmeter or other low
speed device. On the other hand, when C1 is omitted the 10%-
90% response time is under 200 ns, and is typically 300 ns to
99% of final value. T o achieve faster response times, it is neces-
sary to lower the load resistance at the output of the AD8307,
then restore the scale using a higher gain in the op amp. Using
8.33 k
, the basic slope is 10 mV/dB; this can be restored to
25 mV/dB using a buffer gain of 2.5. T he overall 10%-90%
response time is under 100 ns. Figure 37 shows how the output
current capability can be augmented to drive a 50
load; R
T
optionally provides reverse termination, which halves the slope
to 12.5 mV/dB.
Four-Pole Filter
In low frequency applications, for example, audio down to 20 Hz,
it is useful to employ the buffer amplifier as a multipole low-pass
filter, in order to achieve low output ripple while maintaining a
rapid response time to changes in signal level.
INP VPS ENB INT
AD8307
INM COM OFS OUT
INPUT
–75dBm TO
+16dBm
R
S
4.7
V
6
3dB
NC
0.1
m
F
V
P
, 2.7–5.5V
10mV/dB
6
18%
VR2
50k
V
6.34k
V
VR1
5k
V
AD8031
R1
2k
V
R2
3.01k
V
OUTPUT
50
V
MIN
COM
2N3904
NC = NO CONNECT
R
(OPTIONAL)
25mV/dB
(SEE FIGURE 36)
Figure 37. Cable-Driving Log Amp
In Figure 38, the capacitor values were chosen for operation in
the audio field, providing a corner frequency of 10 Hz, an attenua-
tion of 80 dB/decade above this frequency, and a 1% settling
time of 150 ms (0.1% in 175 ms). T he residual ripple is 4 mV
(
±
0.02 dB) when the input to the AD8307 is at 20 Hz. T his
filter may easily be adapted to other frequencies, by proportional
scaling of C5–C7 (e.g., for 100 kHz use 100 pF). Placed ahead
of a digital multimeter, the convenient slope scaling of 100 mV/dB
requires only a repositioning of the decimal point to read directly
in decibels. T he supply voltage for the filter must be large enough
to support the dynamic range; a minimum of 9 V is needed for
most applications; 12 V is recommended.
INP VPS ENB INT
AD8307
INM COM OFS OUT
INPUT
5mV TO
160V rms
COM
0.1
m
F
V
P
VR2
50k
V
SLOPE
32.4k
V
80.6k
V
100k
V
OUTPUT
100mV/dB
NC
OP AMP IS AD8032
SCALE C1 – C8 AS NEEDED
(SEE TEXT). NOTE POLARITIES
IF TANTALUM CAPACITORS
ARE USED.
C4
1
m
F
34k
V
C6
1
m
F
C5
1
m
F
7.32k
V
93k
V
C8
1
m
F
C2
10
m
F
C3
2.5nF
C1
10
m
F
VR1
2k
V
INT
6
4dB
422
V
4.7
V
R1
50k
V
75k
V
C7
1
m
F
34k
V
Figure 38. Log Amp with Four-Pole Low-Pass Filter
Figure 38 also shows the use of an input attenuator which may
optionally be employed here, or in any other of these applica-
tions, to produce a useful wide-range ac voltmeter with direct-
decibel scaling. T he basic range of –73 dBm to +17 dBm (that
is, 50
μ
V rms to 1.6 V rms, for sine excitations) is shifted, for
illustrative purposes, to 5 mV to 160 V rms (at which point the
power in R1 is 512 mW). Because the basic input resistance of
the AD8307 is not precise, VR1 is used to center the signal
range at its input, doubling as a
±
4 dB intercept adjustment.
T he low frequency response extends to 15 Hz; a higher corner
frequency can be selected as needed, by scaling C1 and C2. T he
shunt capacitor C3 is used to lower the high frequency band-
width to about 100 kHz, and thus lower the susceptibility to
spurious signals. Other values should be chosen as needed for
the coupling and filter capacitors.
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參數(shù)描述 |
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| AD8307ARZ | 功能描述:IC LOGARITHMIC AMP 92DB 8-SOIC RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:60 系列:- 類型:可變?cè)鲆娣糯笃?應(yīng)用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
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