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參數(shù)資料
| 型號： | AD607 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Low Power Mixer/AGC/RSSI 3 V Receiver IF Subsystem(低功耗混合器/AGC/RSSI 3V接收器IF子系統(tǒng)) |
| 中文描述： | 低功耗混合機/自動增益控制/ RSSI的3 V接收機中頻子系統(tǒng)（低功耗混合器/自動增益控制/ RSSI的3V的接收器中頻子系統(tǒng)） |
| 文件頁數(shù)： | 18/24頁 |
| 文件大小： | 510K |
| 代理商： | AD607 |
REV. 0
–18–
AD607
As noted earlier, the gain in dB is reduced linearly with the volt-
age V
G
on the GAIN pin. Figure 43 shows how the mixer and
IF strip gains vary with V
G
when GREF is connected to VMID
(1.5 V) and a supply voltage of 3 V is used. Figure 44 shows
how these vary when GREF is connected to a 1.23 V reference.
V
g
(7.5dB)
(1.5dB)
0
1V
2V
0.4V
1.8V
2.2V
(67.5dB)
(21.5dB)
IF GAIN
MIXER GAIN
90dB
80dB
70dB
60dB
50dB
40dB
30dB
20dB
10dB
0dB
NORMAL OPERATING RANGE
Figure 43. Gain Distribution for GREF = 1.5 V
(7.5dB)
(1.5dB)
0
1V
2V
(67.5dB)
(21.5dB)
IF GAIN
MIXER GAIN
90dB
80dB
70dB
60dB
50dB
40dB
30dB
20dB
10dB
0dB
0.328V
1.64V
V
g
NORMAL OPERATING RANGE
Figure 44. Gain Distribution for GREF = 1.23 V
Using the Internal AGC Detector
The AD607 includes a detector cell at the output of the IF am-
plifier that allows it to provide its own AGC and output-leveling
function in receiver applications where DSP support is not
needed. It is only necessary to connect a filter capacitor between
the GAIN pin and ground to invoke this feature. The voltage
appearing on this pin may then be used as an RSSI output, with
the scaling discussed earlier; note particularly that the voltage on
GREF continues to determine this scaling.
Figure 45 shows a simplified schematic of the detector. Transis-
tor Q2 remains cut off by a 300 mV bias (when V
P
= 3 V; in gen-
eral,
≈
V
P
/10) until the positive tip of the IF waveform causes
it to briefly conduct, charging the AGC filter capacitor C
AGC
in
a positive direction. The voltage across this capacitor is V
G
.
LAST IF STAGE
IFOP
1.5V
IF OUTPUT
Q1
Q2
77μA
30μA
4.5μA
ZERO
1.5V + 316mV
I
C
2
GAIN
TO INTERNAL
GAIN CONTROL
CAGC
(EXT)
4.5μA
(INT)
COMM
AVERAGE OF IC2 IS
FORCED TO 4.5μA BY
INTEGRATION IN CAGC
Figure 45. Simplified Schematic of AGC Detector
Acting against this is an internally generated 4.5
μ
A pull-down
current, which operates to within a few millivolts of ground. As
V
G,
the voltage at the GAIN/RSSI pin, rises, the gain falls, so re-
ducing the amplitude of the IF output and reducing the ampli-
tude of the current spike in Q2; eventually a point is reached
where its average collector current is balanced by the pull-down
current, and the charging ceases. It will be apparent that the
loop filter is essentially a perfect integrator.
This simple system can be used because the input impedance of
the gain-control system, also internally tied to the GAIN/RSSI
pin, is several megohms, and its bias current is small. The volt-
age V
G
may be used as an RSSI output; however, if it is to be
heavily loaded, a buffer amplifier must be used.
Note that, unlike a post-demodulation AGC detector (via DSP),
this scheme responds to signal plus noise. Thus, when operating
at high gains, the AGC loop will “see” a substantial output at
the IFOP node, even though a filter may be added by the user
between the pins IFOP and DMIP. This will trick the loop into
lowering the gain until the composite output signal (IF plus
noise) reaches the reference level and satisfies the average-
current requirement. In these circumstances, the wanted signal
will be smaller than expected. Thus, the internal AGC system
will result in a slight compression of the demodulated output for
very small signal levels.
AGC Discharge Time
The discharge current is approximately 4.5
μ
A; thus, to restore
gain in the event of a rapid drop-out requires a time of
T = C
×
V
G
/4.5
μ
A. Using a 1 nF capacitor, and noting that an
80 dB gain change corresponds to 1.6 V, the discharge time is
355
μ
s. Note, however, that when GREF is tied to a different
value, the scaling changes. For GREF = 1.23 V, the scale factor
is 16.4 mV/dB, 80 dB corresponds to a 1.312 V change, and the
discharge time decreases to 290
μ
s.
V
G
could also be expressed in dB: with a scaling of 20 mV/dB, it
works out to T = C
×
P
×
44,000, where P is the change in input
power, expressed in dB. Thus, using C = 1 nF, checking the
time needed for 80 dB we get T = 355
μ
s. For the case where
the scaling is 16.4 mV/dB, T = C
×
P
×
36,000.
The AD607’s AGC detector delivers only one brief charging
pulse per cycle of the IF. At a 10.7 MHz IF, for example, this is
every 93 ns. When the AGC system is in equilibrium, this pulse
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| AD607ARS | 功能描述:射頻混合器 LINEAR IF SUBSYSTEM RoHS:否 制造商:NXP Semiconductors 頻率范圍: 轉換損失——最大: 工作電源電壓:6 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 安裝風格:Through Hole 封裝 / 箱體:PDIP-8 封裝:Tube |
| AD607ARS-REEL | 功能描述:IC RCVR IF SUBSYSTEM 3V 20-SSOP RoHS:否 類別:RF/IF 和 RFID >> RF 其它 IC 和模塊 系列:- 標準包裝:100 系列:* |
| AD607ARSZ | 功能描述:IC LIN RCVR IF SUBSYS LP 20-SSOP RoHS:是 類別:RF/IF 和 RFID >> RF 其它 IC 和模塊 系列:- 標準包裝:100 系列:* |
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