Dual IF Digital Variable Gain Amplifier

10 – 500 MHz IDTF1241NBGI

IDT FlatNoise

20

Rev O Nov 2012

IDTF1241

DATASHEET

O

d

The F1241 can be dropped directly into a 100 ohm termination environment without any topology changes, so

no board redesign is necessary. The example schematic below is for a 153 MHz IF center frequency. Simply

replace the pullup inductors already on the board with 91 nH and replace the series AC coupling capacitors

already on the board with 18 pF. The F1241 in this case will then drive a 100 ohm filter with ~16 dB return

loss. See schematic and measured results when matched to 100 ohms below:

18 pF

18 pF

VGA_OUT+

VGA_OUT-

91 nH

91 nH

CB

5V

153 MHz +/- 20MHz AAF

50

CB

CB

50

CB

V_IN+

V_IN-

Unbuffered

Pipeline ADC

F1240/1

Pullup Inductors:

Coilcraft 0805CS

Pins 24, 23

Pins 18, 17

AC coupling

Capacitor

AC coupling

Capacitor

-25

-20

-15

-10

-5

0

5

10

15

20

25

1.0E+08

1.2E+08

1.4E+08

1.6E+08

1.8E+08

2.0E+08

Frequency (Hz)

S21

S22

15

20

25

30

35

40

45

50

55

-2

0

2

4

6

8

10

12

14

16

18

20

Gain Setting (dB)

134 MHz

174 MHz

154 MHz

-100

-95

-90

-85

-80

-75

-70

-65

-60

-55

-50

-2

0

2

4

6

8

10

12

14

16

18

20

Gain Setting (dB)

134 MHz

174 MHz

154 MHz

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

-4

-2

0

2

4

6

8

10

12

14

16

18

20

Gain Setting (dB)

154 MHz Gain Step Error

154 MHz Absolute Gain Error