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dc1885af

DEMO MANUAL DC1885A

DETAILED DESCRIPTION

Absolute Maximum Ratings

NOTE: Stresses beyond Absolute Maximum Ratings may

cause permanent damage to the device. Exposure to any

Absolute Maximum Rating condition for extended periods

may affect device reliability and lifetime.

Supply Voltage (VCC)...............................................4.0V

IF Supply Voltage (VCC_IF)..................................... 5.5V

Shutdown Voltage (SHDN)............. –0.3V to VCC + 0.3V

LO Input Power (4GHz to 6GHz)............................ 9dBm

RF Input Power (4GHz to 6GHz)...........................15dBm

Supply Voltage Ramping

Fast ramping of the supply voltage can cause a current

glitch in the internal ESD protection circuits. Depending on

the supply inductance, this could result in a supply volt-

age transient that exceeds the maximum rating. A supply

voltage ramp time of greater than 1ms is recommended.

Do not clip powered test leads directly onto the demon-

stration circuit’s VCC and VCC_IF turrets. Instead, make

all necessary connections with power supplies turned off,

and then increase to operating voltage.

Shutdown Feature

When the SHDN voltage is logic Low (<0.3V), the chip is

enabled. When the SHDN voltage is logic High (>3V), the

chip is disabled, and the current consumption is reduced

to below 500μA. The SHDN must be pulled Low or High. If

left floating, the On/Off state of the IC will be indeterminate.

A logic table for the SHDN is shown in Table 2.

Table 2. SHDN Logic Table

SHDN

IC STATE

Low

On

High

Off

RF Input

The RF input of Demonstration Circuit 1885A is matched

to 50Ω from 4.2GHz to 6GHz with better than 12dB return

loss. For the RF input to be matched, the LO input must

be driven. The RF input impedance is somewhat dependent

on LO frequency and, to a lesser extend, LO input power.

LO Inputs

The LTC5544’s LO amplifiers are optimized for the 4.2GHz

to 5.8GHz LO frequency range. LO frequencies above and

below this frequency range may be used with degraded

performance.

The nominal LO input level is 2dBm. The LO input power

range is between –1dBm and 5dBm.

IF Output

Demonstration Circuit 1885A features a single-ended,

50Ω-matched IF output for 240MHz. The impedance

matching is realized with a bandpass topology using an

IF transformer as shown in Figure 1.

4:1

T1

C10

L2

L1

C8

14

15

LTC5544

Figure 1. IF Output with Bandpass Matching

Demonstration Circuit 1885A can be easily reconfigured

for other IF frequencies by simply replacing inductors L1

and L2. L1 and L2 values for several common IF frequen-

cies are presented in Table 3, and return losses are plotted

in Figure 2.

Table 3. L1, L2 vs IF Frequencies

IF FREQUENCY (MHz)

L1, L2 (nH)

140

220

190

150

240

150

305

82

380

56

456

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