Communication Concepts 2M 1KW Amateur Application Note User Manual

Page 9

MRFE6VP61K25H MRFE6VP61K25HS 2 Meter Amateur

RF Reference Design Data

Freescale Semiconductor

HARMONIC MEASUREMENTS

At the one kW level, second harmonic is --42 dBc, third

harmonic is --32 dBc, and fourth harmonic is --37 dBc.

To be used “on the AIR” this amplifier will likely need a filter

to be compliant with local regulations. A diplexer could give

better results than a simple low pass filter because
harmonics are absorbed in a resistive load instead of being
reflected to the transistor.

at e:

4. NOV .20 10

1 6:

Figure 11. Harmonics @ 1 kW

FREESCALE RF POWER 50 V TECHNICAL ADVANTAGES

50 V Drain Voltage

50 volt operation offers benefits over lower voltage

operation because the output impedance of the device for
the same output power is much greater, so the output match
circuitry is simpler and has lower loss. IMD performance is
better and supply current will also be lower than with low
voltage operation.

The reference fixture was designed with the market

standard power supply, allowing the amplifier to utilize a
standard 48 volt power supply (most are adjustable from 43
to 54 volts).

Extended Gate Voltage Range

The

enhanced

electro--static

discharge

protection

structure at the gate of the transistor is a Freescale
innovation pioneered in the cellular infrastructure market that
is incorporated into the 50 V LDMOS RF power product
portfolios. This ESD structure can tolerate moderate reverse
bias conditions applied to the gate lead up to --6 volts (see
Figure 12). This allows Freescale transistors to be used in
applications where the gate voltage needs to be set as low
as --6 volts.

This feature can dramatically simplify protection circuits,

as it allows the transistor to be shut down because of high
VSWR or PLL unlock without shutting down the drive power.

Setting the gate bias voltage to around --4 volts will totally

block the transistor even if the RF input signal is still there.

Figure 12. Gate Voltage Breakdown with ESD

2.E--02

0.E+00

--2.E--02

--1.E--02

--5.E--03

5.E--03

1.E--02

--15

--10 --5

5 10 15

(V)

ESD

)

Enhanced ESD