SA5204AD PHILIPS [NXP Semiconductors], SA5204AD Datasheet - Page 7

• Manufacturer Part Number: SA5204AD
• Description: Wide-band high-frequency amplifier
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
THEORY OF OPERATION
The design is based on the use of multiple feedback loops to
provide wide-band gain together with good noise figure and terminal
impedance matches. Referring to the circuit schematic in Figure 17,
the gain is set primarily by the equation:
which is series-shunt feedback. There is also shunt-series feedback
due to R
impedances without the need for low value input shunting resistors
that would degrade the noise figure. For optimum noise
performance, R
possible, while R
The noise figure is given by the following equation:
NF
where I
R
The DC input voltage level V
where R
at V
Under the above conditions, V
Level shifting is achieved by emitter-follower Q
which provide shunt feedback to the emitter of Q
of an emitter-follower buffer in this feedback loop essentially
1992 Feb 25
V
V
0
V
OUT
=50 for a 50 system and 75 for a 75 system.
Wide-band high-frequency amplifier
IN
IN
CC
=V
=6V).
C1
10Log
BE1
E1
F2
=5.5mA, R
=12 , V
(R
and R
+(I
F1
C1
E1
1
F2
+I
E2
and the base resistance of Q
BE
C3
R
is maximized.
which aids in producing wide-band terminal
E1
E1
) R
=0.8V, I
=12 , r
)
r
E1
b
(3)
R
IN
E1
R
C1
b
IN
E1
R
can be determined by the equation:
=130 , KT/q=26mV at 25 C and
=5mA and I
is approximately equal to 1V.
O
V
IN
2ql
KT
C1
3nH
L1
C3
=7mA (currents rated
dB
3
1
and diode Q
1
are kept as low as
via R
Q1
F1
RE1
Figure 17. Schematic Diagram
650
R1
12
. The use
140
RF1
4
,
Q3
(1)
(2)
V
CC
Q4
RF2
200
7
eliminates problems of shunt-feedback loading on the output. The
value of R
DC output voltage V
where V
From here, it can be seen that the output voltage is approximately
3.1V to give relatively equal positive and negative output swings.
Diode Q
R
operating point of the amplifier.
The output stage is a Darlington pair (Q
the DC bias voltage on the input stage (Q
value, and also increases the feedback loop gain. Resistor R
optimizes the output VSWR (Voltage Standing Wave Ratio).
Inductors L
roughly 3nH. These improve the high-frequency impedance
matches at input and output by partially resonating with 0.5pF of pad
and package capacitance.
POWER DISSIPATION CONSIDERATIONS
When using the part at elevated temperature, the engineer should
consider the power dissipation capabilities of each package.
At the nominal supply voltage of 6V, the typical supply current is
25mA (32mA max). For operation at supply voltages other than 6V,
see Figure 3 for I
inversely proportional to temperature and varies no more than 1mA
between 25 C and either temperature extreme. The change is 0.1%
per C over the range.
The recommended operating temperature ranges are air-mount
specifications. Better heat-sinking benefits can be realized by
mounting the SO and N package bodies against the PC board
plane.
F2
V
OUT
to the base of Q
=V
CC
5
is included for bias purposes to allow direct coupling of
F1
CC
=6V, R
1
Q6
=140 is chosen to give the desired nominal gain. The
R3
140
and L
225
–(I
R2
C2
CC
2
+I
Q5
2
=225 , I
R0
10
Q2
RE2
12
OUT
C6
are bondwire and lead inductances which are
versus V
1
. The dual feedback loops stabilize the DC
)R2,(4)
can be determined by:
3nH
L2
C2
CC
=8mA and I
curves. The supply current is
V
OUT
6
and Q
C6
1
NE/SA5204A
) to a more desirable
=5mA.
2
Product specification
) which increases
SR00209
0