13-66
TA0012
13
Copyright 1997-2000 RF Micro Devices, Inc.
tance formed by the output bond wires, leads, and
microstrip, and two shunt capacitors external to the
part. With this match, a 50
Ω terminal impedance is
achieved. The input is matched to 50
Ω with just a
blocking capacitor needed. The input is DC coupled;
thus, a blocking cap must be inserted in series.
Vcc1 provides supply voltage to the first stage, as well
as provides some control over the operating band.
Essentially, the bias is fed to this pin through a short
transmission line. A tuning capacitor external to Pin 1
sets the frequency of the gain peak. A resistor in paral-
lel with the bias choke for the first stage helps to stabi-
lize and dequeue the circuit.
The RFout pins provide the output power. Pins 12 and
13 should be combined externally. Bias for the final
stage is fed to this output line, and the feed must be
capable of supporting the 1-1.5A of current required.
The HBT breakdown voltage is >20V, so nominally at
6V there should be no issue with overvoltage. Under
extreme conditions, however, which can occur in a cel-
lular handset environment, the supply voltage could be
as high as 8.5V to 9.5V. These conditions may corre-
spond to operation in a battery charger, especially with
the battery removed, which “unloads” the supply cir-
cuit. To add to this worst-case scenario, the RF drive
may be at full power during transmit, and the output
VSWR could be extremely high, corresponding to a
broken or removed antenna. Under all of the above
conditions, the peak RF voltages could well exceed 2X
the supply voltage, forcing the device into breakdown.
The RF2123 includes overvoltage protection diodes at
the output, which begin clipping the waveform peaks at
~15 V. This protects the device’s output from breaking
down under these worst-case conditions, and provides
a rugged, robust component for the system designer.
High current conditions are also potentially dangerous
to any RF device. High currents lead to high channel
temperatures and may force early failures. The
RF2123 includes reference diodes in the bias circuit to
temperature compensate the RF transistors, thus limit-
ing the current through the bias network and protecting
the devices from damage. The same mechanism
works to compensate the currents due to ambient tem-
perature variations, and the part is remarkably consis-
tent
over
the
full
-30°C
to
+85°C
commercial
temperature range.
While the part is safe under CW operation, maximum
power and reliability will be achieved under pulsed con-
ditions. The data shown in the following table were
taken with a 12.5% duty cycle and a 600ms pulse.
! "
The RF2123 performance is summarized in Table 1
below. A full data sheet is available from RF Micro
Devices.
$
The RF2123 HBT GSM Cellular Power Amplifier has
been introduced by RF Micro Devices. This amplifier
provides the best overall performance of any integrated
PA on the commercial market. Operating from a single
positive supply, efficiencies of 55% and power levels of
4-W are achievable from a single 16-lead SOIC surface
mount package at 6V. Power down and power control
are integrated on-chip without additional components
required. The new power amplifier can be used to sim-
plify cellular phone design and improve operation, as
well as significantly reducing overall cost.
Table 1. RF2123 Performance Summary
Parameter
Typical Performance Conditions
Frequency Range
890-915 MHz
Maximum CW Output Power
4-W
With specified load at 6V
Total CW Efficiency
55%
at Max Output
Gain at Max Power
30 dB
Gain Control Range
45 dB, min
Vpc Current
1 mA, max
“OFF” Current
10 uA, max
Vpc < 0.2V
Voltage Range
5.3 to 6V
Stability
Spurious <-60dBm
Output VSWR < 8:1
Temperature Range
-30 to +85 C
Operating
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