Cellular CDMA Mixer Performance with the MAX2538 and KSS IF Filter


The application note presents measured performance of the MAX2538 low-noise amplifier (LNA) mixer IC when matched to a 183.6MHz IF from Kinseki (KSS). Cascade performance is shown, along with the schematic for the IF matching circuit. IIP3 was found to be +9.2dBm.

Additional information:


This application note summarizes the MAX2538 cellular CDMA (code division multiple access) mixer performance when it is matched to a IF (intermediate frequency) SAW (surface acoustic wave) filter at 183.6MHz (7mm x 5mm package). The particular filter used is KSS part number MSFC30-183-001M0.

The cellular CDMA mixer/IF filter signal path gain, NF (noise figure), and IIP3 (input third order intercept) have been optimized based on gain, IIP3, passband flatness, and adjacent channel selectivity. Cascaded performances have been characterized and are presented here. The MAX2538 clearly demonstrates excellent NF and IIP3 performance for cellular CDMA applications.

Cascaded IIP3 in HGHL (high gain, high linearity) mode achieved is:

(62.5dBc/2) + (-22dBm) = +9.2dBm

Refer to circuit diagram for component values and plots for test measurement data.

Cellular CDMA Mixer/IF Filter Cascaded Performance

The MAX2538 is configured in cellular HGHL mode. The supply voltage (VCC) is set at +2.80V. The test platform is a multi-layer PCB (printed circuit board) which employs the KSS IF CDMA filter. The block diagram is shown in Figure 1 while measured cascade performance data are shown in Table 1.

Figure 1. Cascaded MAX2538 mixer block diagram in cellular mode.
Figure 1. Cascaded MAX2538 mixer block diagram in cellular mode.

The MAX2538 Mixer and SAW Filter Impedance Characteristics

SAW Filter
KSS MSFC30-183-001M0
MAX2338 IF Port Differential Equivalent Circuit
12.2kΩ || 0.75pF
MAX2338 IF External Load
Equivalent Differential Source Impedance presented to SAW Filter
2.2kΩ || 0.75pF
Single-ended Load Impedance presented to SAW Filter
SAW Filter Input Source Impedance
788Ω || -9.8pF
SAW Filter Output Source Impedance
855Ω || -7.5pF

The MAX2538 Cellular Mixer Cascaded Gain and IIP3 Measured Data

RF Frequency = 880.98MHz and 881.04MHz at -22dBm per tone.
LO Frequency = 2129.2MHz.
IF = 183.6MHz Mode = High Gain High Linearity (HGHL), IF0 port selected
VDD_RX = +2.80V

Table 1. HGHL Mode Performance Results

IF SAW and
Matching Loss
Gain (db)
IIP3 (dBm)
NF (dB)
*Estimated IF filter insertion loss based on measured cascaded gain of +3.0dB and mixer standalone gain of 12dB.

ΔIM3 = -62.5dBc at the IF output

IIP3 = 62.5/2 + (-22dBm) = +9.2dBm

PIN = -22dBm per tone at 881 and 881.2MHz

POUT = -18.0dBm

Cascaded Gain = +3.0dB

Cellular CDMA Mixer and IF SAW Filter Frequency Swept Response

Cascaded MAX2538 cellular mixer and KSS IF filter response:

The MAX2538 Mixer Matching Circuit Components

Matching components are shown in the following figure: