3

The LT5502 has two reduced-power modes of operation. In shutdown mode, power is reduced

to less than 1µA. In standby mode with current consumption of 2.6mA, the baseband outputs

are pre-biased at their nominal quiescent voltages. This allows instant turn-on with no delay

when the LT5502 is interfaced to a baseband chip using large coupling capacitors.

Applications and implementation issues

IF input external circuitry

The external IF input circuitry to the LT5502 can be configured in several different ways,

depending on cost, available board space and performance considerations.

1:4 RF transformer (Figure 3a)

A 1:4 RF transformer with a 240-ohm resistor in the secondary provides a broadband 50-ohm

impedance match at the primary. A Mini-Circuits JTX-4-10T 1:4 RF transformer or similar

transformers from other manufacturers can be used. The cascaded NF is degraded by the

transformer loss (1.0 to 2.0 dB). A 1:1 RF transformer can also be used with a 51 to 62 ohm

terminating resistor in the secondary of the transformer.

Direct 50-ohm termination (Figure 3b)

This circuit offers a simple and economical solution for single-ended-to-differential

conversion, although with a penalty of reduced sensitivity. A 62 ohm resistor provides

broadband 50-ohm impedance matching. The cascaded NF for the IF circuit is degraded by

2.0 dB. Figure 1 shows a version of the demo board DC333A with 62 ohm terminating

resistor.

22 nF

62 ohm

22 nF

IF Input

To LT5502

6

7

22 nF

240 ohm

1:4 RF

transformer

IF input

To LT5502

6

7

Figure 3a

Figure 3b