Philips Semiconductors

Product specification

NE/SA5204A

Wide-band high-frequency amplifier

1992 Feb 25

7

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:

V

OUT

V

IN

+ (R

R

E1

(1)

which is series-shunt feedback. There is also shunt-series feedback

impedances without the need for low value input shunting resistors

that would degrade the noise figure. For optimum noise

The noise figure is given by the following equation:

NF

+ 10Log 1 )

r

KT

2ql

C1

R

O

dB

(2)

of an emitter-follower buffer in this feedback loop essentially

eliminates problems of shunt-feedback loading on the output. The

From here, it can be seen that the output voltage is approximately

3.1V to give relatively equal positive and negative output swings.

operating point of the amplifier.

optimizes the output VSWR (Voltage Standing Wave Ratio).

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,

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.

VIN

L1

3nH

Q1

Q4

RF1

140

RE1

12

RF2

200

Q5

RE2

12

R3

140

Q6

10

3nH

L2

VOUT

R2

225

VCC

R1

650

R0

Q3

Q2

SR00209

Figure 17. Schematic Diagram