LT5504

7

5504i

OUTPUT CURRENTS

FROM RF AND IF

DETECTORS

400

µA

5504 F04

+

–

TYPICAL APPLICATIO S

Limiting Mixer and LPF

The amplified RF signal is down-converted using the

limiting mixer and LO signal. The resulting signal is filtered

by the 3rd-order, 450MHz, integrated low pass filter (LPF).

Only the desired IF signal is passed to the IF limiters for

further detection. Any other mixing products, including LO

feedthrough, are much reduced to maximize sensitivity.

The receiver’s sensitivity is thus defined by the LPF band-

width.

IF Limiter

The IF signal is then amplified through the multiple limiter

stages for further signal detection. All DC offsets, includ-

ing LO signal self-mixing, are eliminated by an internal DC

offset cancellation circuit. Nevertheless, care should be

taken in component placement and in PCB layout to

minimize LO coupling to the RF port.

Output Interface

The output interface of the LT55O4 is shown in Figure 4.

The output currents from the RF and IF detectors are

The maximum charging current available to the output

load is about 400

µA. An internal compensation capacitor

capacitive output load. The slew rate is 80V/

µs and the

small signal output bandwidth is approximately 5MHz

when the output is resistively terminated. When the output

APPLICATIO S I FOR ATIO

Figure 5. LT5504 Evaluation Board Circuit Schematic

Figure 6.Component Side Silkscreen of Evaluation Board

5504 F04

1

2

3

4

8

7

6

5

GND

LO

EN

C2

100pF

C3

1nF

C7

100pF

LO

INPUT

R1

82

Ω

R3

10k

R2

200

Ω

R5

500k

R4

20k

C1

100pF

C4

1nF

RF

INPUT

LT5504

JUMPER

T1

TOKO

617DB-1022

to 400

Figure 4. Simplified Circuit Schematic of the Output Interface

Applications

The LT5504 can be used as a self-standing signal strength-

measuring receiver (RSSI) for a wide range of input

signals from – 75dBm to +5dBm, for frequencies from

800MHz to 2.7GHz.

The LT5504 can be used as a demodulator for AM and ASK

modulated signals with data rates up to 5MHz. Depending

on specific application needs, the RSSI output can be split

into two branches, providing AC coupled data output, and

DC coupled, RSSI output for signal strength measure-

ments and AGC. Refer to Figure 5.

The LT5504 can also be used as a wide range RF power

detector for transmit power control.