RF2860 datasheet(14/20 Pages) RFMD

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RF2860

Rev A9 DS050902

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

lized 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 filter. 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 start-

ing 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 resonate circuit (C2,

L2 and L3) and the resistor (R) for optimal performance. After optimal performance is achieved and if performance is not satis-

factory, decrease the series capacitors until optimal performance is achieved.

Single-End IF Matching

VCC

100 pF

IF+

IF-

IF Saw

IF-

IF+

RF2860 Datasheet(PDF) 14 Page - RF Micro Devices