Measurement Results for the Dynamic Supply CMOS RF Power Amplifie - Linear CMOS RF Power Amplifiers for Wireless Applications - page 44

Fig. 4.6 Envelope processing circuit including envelope detection

Table 4.2 Envelope
processing circuit details

Component Value

R 1 68

R 2 68

R 3 50

R 4 175

R f 330

C 1 18 pF

C 2 100 pF

VCC 5 V

PCB and used together with the main evaluation board in the characterization of the
dynamic supply RF PA.
In the detector of Fig. 4.6 , R 1 is a termination resistor 4 and C 1 is a coupling
capacitor [ 16 ]. R 2 and C 2 form a low-pass output filter with a cutoff frequency of
around 20 MHz. A single power supply of 5 V is used for the LTC5508 power
detector.
In the envelope amplifier of Fig. 4.6 , a dual power supply of

5 V is used. R 3
is a termination resistor and R 4 is an input bias current canceling resistance for
the OPA690 operational amplifier, as indicated in its datasheet [ 5 ]. R f is selected
to be between the values suggested by the operational amplifier's manufacturer
(200 <R f < 1 . 5k and R f //P gain < 300 ) while being able to provide a gain

±

4 68 in parallel with the 250 internal termination of the LTC5508 results in a termination of
about 50 seen by the coupler.