Design of the Frequency-Tunable CMOS RF Power Amplifie - Linear CMOS RF Power Amplifiers for Wireless Applications - page 94

Fig. 6.15 Load-pull contours at 5.2 GHz

Fig. 6.16 π -matching
network used to simulate the
variation of α and β

The output π -matching network is then simulated at 3.7 and 5.2 GHz. To make it
possible to sweep the values of α and β , the tunable inductor is replaced by its equiv-
alent resistance and inductance, whose expressions are given in (5.9) and (5.11)on
p. 69, as shown in Fig. 6.16 . The ranges of α and β are adjusted so that the trans-
formed impedance Z opt falls inside the IMD3 and output power contours as depicted
in Figs. 6.14 and 6.15 . For 3.7 GHz, the ranges are 0 . 6 <α< 1 . 4 and 0 . 2 <β< 1 . 1,
and for 5.2 GHz they are 0 <α< 0 . 5 and 0 <β< 0 . 4.
To verify if the values of α and β can be achieved with the conceptual circuit of
Fig. 6.9 , an AC simulation is performed sweeping the bias voltage V bias2 of transistor
M 2 and its width W 2 . The main results from this simulation are summarized in
Table 6.8 , where I ctrl _ q is the quiescent control current. Therefore, we conclude that
the conceptual circuit can be used.

6.4.4 Complete System

The complete system is shown in Fig. 6.17 . A cascode structure ( M 2 - M 3 ) replaces
the simple transistor M 2 of Fig. 6.9 . This decreases the feedback from the node v y
(see Fig. 6.12 ) to the input of the circuit. The input impedance matching network
comprising L 3 and C 3 in an L -type low-pass matching section is also shown.