AN 074 Rev E

14 / 24

19-November-2002

Applications Note No. 074

Silicon Discretes

Figure 21. Simulated Return Loss and Insertion Loss for 2 – Element High Pass Filter. Note

insertion loss = 10.3 dB at 950 MHz.

The entire amplifier with the high pass filter was

optimized

in

simulations.

A

significant

improvement in I.F. amplifier gain slope was

achieved. Please refer to Figures 22 – 29 for

Return Loss, Gain and Reverse Isolation plots of

the complete BGA430 + BGB540 I.F. Amplifier,

with and without the I.F. Amp driving a 30 meter

length of coaxial cable.

For the complete I.F. Amplifier, there is a

difference of about 4 dB in gain between 950

and 2150 MHz, with a positive slope – and

that the 30.4 meter / 100 foot length of 75

ohm coaxial cable has about a 4 dB

difference in insertion loss between 950 and

2150 MHz, with a negative slope.

To see the net gain response of the gain-sloped

BGA430 + BGB540 I.F. Amplifier together with

30.4 meters / 100 feet of 75 ohm coaxial cable,

this combination was measured in a network

analyzer. Please refer to Figure 23 on page 16.

A plot of the resulting gain response of the

complete gain-sloped BGA430 + BGB540 I.F.

Amp driving 30 meters / 100 feet of coaxial

cable is given. When this I.F. Amp drives 30

meters of 75 ohm coax, the gain at 950 and

2150 MHz is virtually identical, with a 3 dB

‘hump’ or rise at mid band.

The use of a high pass filter to achieve a

positive gain slope does limit the available

output compression point at the lower end of the

frequency range (950 MHz). However, some of

the output power capability could be bought

back by running the BGA430 at a higher bias

voltage than 5.0 volts as is done here, since the

BGA430 can safely tolerate up to 6.5 volts.