16

LT1630/LT1631

16301f LT/TP 0998 4K • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 1998

RF Amplifier Control Biasing and DC Restoration

Taking advantage of the rail-to-rail input and output, and

the large output current capability of the LT1630, the

circuit, shown in Figure 6, provides precise bias currents

for the RF amplifiers and restores DC output level. To

ensure optimum performance of an RF amplifier, its bias

point must be accurate and stable over the operating

temperature range. The op amp A1 combined with Q1, Q2,

R1, R2 and R3 establishes two current sources of 21.5mA

to bias RF1 and RF2 amplifiers. The current of Q1 is

determined by the voltage across R2 over R1, which is

replicated in Q2. These current sources are stable and

precise over temperature and have a low dissipated power

due to a low voltage drop between their terminals. The

amplifier A2 is used to restore the DC level at the output.

With a large output current of the LT1630, the output can

be set at 1.5VDC on 5V supply and 50

Ω load. This circuit

has a 3dB bandwidth from 2MHz to 2GHz and a power gain

of 25dB.

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

A1

1/2 LT1630

1630/31 F06

5V

5V

HP-MSA0785

HP-MSA0785

R3

10k

L1

220

µH

C5

0.01

µF

L2

220

µH

Q1

2N3906

Q2

2N3906

C6

0.01

µF

R5

50

Ω

R1

10

Ω

R2

453

Ω

R4

10

Ω

C3

1500pF

–

+

A2

1/2 LT1630

C4

1500pF

C2

1500pF

C1

0.01

µF

L4

3.9

µH

L3

3.9

µH

+

+

+

RF1

RF2

Figure 6. RF Amplifier Control Biasing and DC Restoration

RELATED PARTS

PART NUMBER

DESCRIPTON

COMMENTS

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Dual/Quad 14MHz, 7V/

µs, Single Supply Precision Op Amps

Input Common Mode Includes Ground, 275

6

µV/°C Max Drift, Max Supply Current 1.8mA per Op Amp

LT1213/LT1214

Dual/Quad 28MHz, 12V/

µs, Single Supply Precision Op Amps

Input Common Mode Includes Ground, 275

6

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LT1215/LT1216

Dual/Quad 23MHz, 50V/

µs, Single Supply Precision Op Amps

Input Common Mode Includes Ground, 450

6

µV/°C Max Drift, Max Supply Current 6.6mA per Op Amp

LT1498/LT1499

Dual/Quad 10MHz, 6V/

µs Rail-to-Rail Input and Output

High DC Accuracy, 475

C-Load

Max Supply Current 2.2mA per Amp

LT1632/LT1633

Dual/Quad 45MHz, 45V/

µs Rail-to-Rail Input and Output Op Amps

Max Supply Current 5.2mA per Amp

C-Load is a trademark of Linear Technology Corporation.