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參數(shù)資料
| 型號(hào)： | 935056440623 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 放大器 |
| 英文描述： | RF/MICROWAVE WIDE BAND LOW POWER AMPLIFIER |
| 封裝： | SOT109-1, MS-012AC, SO-16 |
| 文件頁數(shù)： | 17/21頁 |
| 文件大?。?/td> | 243K |
| 代理商： | 935056440623 |
Philips Semiconductors
Product specification
SA5219
Wideband variable gain amplifier
1997 Nov 07
5
maximum control voltage frequency of about 20MHz permits video
baseband sources for AM.
A stabilized bandgap reference voltage is made available on the
SA5219 (Pin 7). For fixed gain applications this voltage can be
resistor divided, and then fed to the gain control terminal (Pin 8).
Using the bandgap voltage reference for gain control produces very
stable gain characteristics over wide temperature ranges. The gain
setting resistors are not part of the RF signal path, and thus stray
capacitance here is not important.
The wide bandwidth and excellent gain control linearity make the
SA5219 VGA ideally suited for the automatic gain control (AGC)
function in RF and IF processing in cellular radio base stations,
Direct Broadcast Satellite (DBS) decoders, cable TV systems, fiber
optic receivers for wideband data and video, and other radio
communication applications. A typical AGC configuration using the
SA5219 is shown in Figure 3. Three SA5219s are cascaded with
appropriate AC coupling capacitors. The output of the final stage
drives the full-wave rectifier composed of two UHF Schottky diodes
BAT17 as shown. The diodes are biased by R1 and R2 to VCC such
that a quiescent current of about 2mA in each leg is achieved. An
SA5230 low voltage op amp is used as an integrator which drives
the VAGC pin on all three SA5219s. R3 and C3 filter the high
frequency ripple from the full-wave rectified signal. A voltage
divider is used to generate the reference for the non-inverting input
of the op amp at about 1.7V. Keeping D3 the same type as D1 and
D2 will provide a first order compensation for the change in Schottky
voltage over the operating temperature range and improve the AGC
performance. R6 is a variable resistor for adjustments to the op
amp reference voltage. In low cost and large volume applications
this could be replaced with a fixed resistor, which would result in a
slight loss of the AGC dynamic range. Cascading three SA5219s
will give a dynamic range in excess of 60dB.
The SA5219 is a very user-friendly part and will not oscillate in most
applications. However, in an application such as with gains in
excess of 60dB and bandwidth beyond 100MHz, good PC board
layout with proper supply decoupling is strongly recommended.
Q1
Q2
VCC
Q3
Q4
Q5
Q6
VBG
BANDGAP
REFERENCE
OUTA
OUTB
Q8
Q7
A1
VAGC
0–1V
I1
I2
I3
50
50
R1
R2
R3
R4
INA
INB
+
–
SR00274
Figure 2. Equivalent Schematic of VGA
RF/IF
INPUT
AGC
OUTPUT
BAT 17
5219
R4
C4
D1
D2
D3
R6
R1
R2
L1
L2
R3
C3
R5
5230
+
–
VCC
SR00275
Figure 3. AGC Configuration Using Cascaded SA5219s
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