Specifications and information are subject to change without notice

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Page 4 of 5

December 2006

VG112

PCS/UMTS-band Variable Gain Amplifier

Application Note: Reduced Bias Configurations

The VG112 can be configured to be operated with lower bias current by varying the bias-adjust resistors – R3 and R4 – which

set the current draw for the two stages of the amplifier. The recommended circuit configurations shown previously in this

datasheet have the device operating in Class A operation. Lowering the current moderately can be done at the expense of the

linearity performance of the device.

Measured data is given below and represents the VG112 configured for 2.14 GHz

applications.

Since the second stage amplifier dominates the current draw of the 2-stage amplifier inside the VG112,

modifying R3 will have the greatest effect upon the overall current draw of the device. Data is shown though to display the Icc

and performance effects of the device when R4, the bias-adjust resistor for the first-stage amplifier, is modified when R3 is

fixed.

Performance Data at 2.14 GHz

R3

( )

R4

( )

Icq

(mA)

(W)

Gain

(dB)

OIP3

(dBm)

P1dB

(dBm)

75

0

436

2.18

24.0

46.3

30.7

174

0

304

1.52

23.7

42.5

30.8

383

0

207

1.04

23.3

33.4

30.9

787

0

155

0.78

22.5

27.7

29.7

174

101

284

1.42

23.5

42.3

30.6

174

270

264

1.32

23.3

41.6

30.4

174

499

251

1.26

23.0

40.2

29.8

174

699

244

1.22

22.7

38.9

29.1

Current vs. R3 Value

200

250

300

350

400

450

0

100

200

300

400

R3 Value (Ohms)