QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1048A

1.5GHZ TO 2.7GHZ DIRECT CONVERSION I/Q RECEIVER

2

APPLICATION NOTE

ABSOLUTE MAXIMUM INPUT RATING

Power Supply Voltage ..........................................5.5V

Enable Voltage .............................. –0.3V to V

CC + 0.3V

RF Input Power................................................ 20dBm

LO Input Power................................................ 10dBm

RF Input DC Voltage ...........................................±0.1V

LO Input DC Voltage ...........................................±0.1V

FREQUENCY RANGE

Demonstration circuit 1048A is designed for evaluating

the LT5575 in the frequency range between 1.5GHz and

2.7GHz. In this frequency range, both of the LT5575’s

RF and LO ports are internally matched to 50

Ω

Ω

Ω

Ω. Below

1.5GHz, a shunt capacitor to ground placed close to the

RF and LO pins of the IC can be used to provide imped-

ance matching to maintain best performance. Matching

capacitor values for different frequency bands are listed

in Table 2.

Table 2. RF and LO match and Baseband Output Filtering

RF Match

LO Match

Baseband

Frequency Range

C10

C12

C1-C4

Low Band:

800 to 1000MHz

4.7pF

3.9pF

10pF

Mid Band:

1000MHz to 1500MHz

2pF

2pF

2.2pF

High Band:

1500MHz to 2700MHz

None

None

None

OUTPUT FILTERING

Proper filtering of unwanted high frequency mixing

products at the I and Q outputs is important to maintain

superior linearity. The most convenient method is to

terminate each output with a shunt capacitor to ground.

The capacitor value should be optimized depending

upon the operating frequency. However, the capacitors

may reduce baseband output bandwidth. Filtering ca-

pacitor values for different frequency bands are listed in

Table 2.

TEST EQUIPMENT AND SETUP

Refer to Figure 1 for proper measurement equipment

setup.

Use high performance signal generators with low

harmonic output for 2-tone measurements. Other-

wise, low-pass filters at the signal generator outputs

should be used to suppress higher-order harmonics.

High quality combiners that provide broadband 50

Ω

Ω

Ω

Ω

termination on all ports and have good port-to-port

isolation should be used. Attenuators on the outputs

of the signal generators are recommended to further

improve source isolation, to prevent the sources

from modulating each other and generating inter-

modulation products.

Spectrum analyzers can produce significant internal

distortion products if they are overdriven. Generally,

spectrum analyzers are designed to operate at their best

with about –30dBm to -40dBm at their input. Sufficient

spectrum analyzer input attenuation should be used

to avoid saturating the instrument.

Before performing measurements on the DUT, the

system performance should be evaluated to ensure

that: 1) a clean input signal is obtained and 2) the

spectrum analyzer internal distortion is minimized.