RF2860PCBA datasheet(9/12 Pages) RFMD

9 / 12 page

8-391

RF2860

Rev A7 031105

Differential IF Matching

L2, L3 and C2 are chosen to resonate at the desired IF frequency. C2 can be omitted and the value of L1 increased and

utilized solely as a choke to provide VCC to the open-collector outputs, but it is strongly recommended that at least some

small-valued C2 (a few pF) be retained for better mixer linearity performance. R1 is normally selected to match the input

impedance of the IF filter. However, mixer performance can be modified by selecting an R value that is different from the

IF filter input impedance, and inserting a conjugate matching network between the Resistive Output Network and the IF

filter.

C1 and C3 serve dual purposes. C1 and C3 serve as a series DC block when a DC path to ground is present in the IF fil-

ter. In addition, C1 may be chosen to improve the combine performance of the mixer and IF filter. L1 should choose to

resonate with the internal capacitance of the SAW filter. Usually, SAW filter has some capacitance. Otherwise, L1 could

be eliminated.

A practical approach to obtain the differential matching is to tune the mixer to the correct load point for gain, IIP3, and NF

using the single-end current combiner method. Second, use the component values found in the single-end approach as

starting point for the differential matching. The two-shunt capacitors in the single-end matching could be converted to a

parallel capacitor and the parallel inductor in the single-end matching needs to be converted in to a choke inductor. Third,

set the DC block capacitors (C1 and C3) in the differential-end matching to a high value (i.e., 100pF) and retune the res-

onate circuit (C2, L2 and L3) and the resistor (R) for optimal performance. After optimal performance is achieved and if

performance is not satisfactory, decrease the series capacitors until optimal performance is achieved.

100 pF

IF+

IF-

IF Saw

IF-

IF+

RF2860PCBA Datasheet(PDF) 9 Page - RF Micro Devices