Measurement Results for the Frequency-Tunable CMOS RF Power Amplifie - Linear CMOS RF Power Amplifiers for Wireless Applications - page 113

Fig. 7.19 Measurement results for the tunable PA for a narrow frequency sweep

7.5 Hybrid Implementation

The circuit of a hybrid implementation of the tunable RF PA is shown in Fig. 7.20 .
It was designed for the 200 and 300 MHz frequency bands—tuning range of 40%.
We used the stand-alone CMOS PA described in Sect. 7.2 biased in class AB with
a quiescent drain current of 25 mA. The input and output matching networks,
the RF choke, and the control circuit were implemented with discrete compo-
nents.
Inductors L 1 and L 2 were implemented with the 1812WBT-5L RF trans-
former [ 5 ], having a winding inductance of 90 nH, a coupling factor of unity, and
a series parasitic resistance of 0 . 15 . The high values of winding inductances for
the available commercial transformers limited the frequency of operation of the cir-
cuit and the minimum value of R opt . The bipolar transistor BFP405 [ 7 ] was used to
implement the control circuit with a quiescent collector current of 1.5 mA.
The target output power was set to 10 dBm and an optimum resistance of 150
was calculated using the loadline method. Load-pull simulations were also used to
determine the values that the load impedance could take. C 1 = 12 pF and C 2 =

18 pF provide the desired load impedance when 50 nH <L eff < 67 nH at 200 MHz
and 29 nH <L eff < 36 nH at 300 MHz. L adj is used to set the value of L eff , and
equals 220 nH at 200 MHz and 51 nH at 300 MHz.