–
TX buffer amplifier provides 16 dB power gain by Q111.Adjust the bias circuit of TX buffer amplifier
circuit to get a quiescent bias current of 28 mA for Q111. Power supply for the switching transistor
Q810 is controlled by TX signal, so as to further control the power supply for the whole circuit.
Pre-driver Power Amplifier
The pre-driver power amplifier is formed by Q805, with variable gain controlled by voltage VGG. The
input matching circuit is composed of C826, L826, L814, C843 and R824.
Driver Power Amplifier
The driver power amplifier is formed by Q804, with variable gain controlled by voltage VGG. Its
maximum output power is 38.5 dBm and maximum gain is 11 dB.
Final-stage Power Amplifier
The final-stage power amplifier outputs via two LDMOS PA transistors (Q802 and Q803) which are in
parallel connection. It can reduce the Q value of the PA input/output match network and expand the
bandwidth of the PA circuit, ensuring the PA circuit’s performance. Both Q802 and Q803 are
controlled by the same bias network. Their static bias current can be adjusted via software to ensure
output consistency.
Antenna Switch
The antenna switch is used to switch between the transmitter circuit and the receiver circuit.
In TX mode
TX signal controls the switching transistor Q810, to further control the power supply (9 V 3 A) for the
PIN diodes D801 and D802. Quiescent bias current of the PIN diode is controlled by the resistors
R821 and R825. In this mode, D801 and D802 are turned on; RF signals are transmitted via the
antenna port through the low-pass filter (composed of C836, C837, C994, C830, C973, C838, C992,
L809, L813, and L810).
In RX mode
TX signal controls the switching transistor Q810, to further control the power supply for the
PIN diodes D801 and D802, which are not applied with DC bias current. When the two PIN diodes
are turned off, signals feed into the RX path through the low pass filter (composed of L827, C852,
and C995).
Low-pass Filter
The low-pass filter consisting of inductors (L809, L813, and L810) and capacitors (C836, C837, C994,
C830, C973, C838, and C992), is used to attenuate harmonic energy from the transmitter.
Directional Coupler
The directional coupler is composed of components such as microstrip directional coupler, D803 and
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