LT5504 Просмотр технического описания (PDF) - Linear Technology

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LT5504

800MHz to 2.7GHz RF Measuring Receiver

Linear Technology 

LT5504

PI FU CTIO S

VCC (Pins 1, 8 ): Power Supply Pins. These pins must be

tied together at the part as close as possible, and should

be decoupled using 1000pF capacitors.

RF+ (Pin 2): Positive RF Input Pin.

RF– (Pin 3): Negative RF Input Pin.

GND (Pin 4): Ground Pin.

EN (Pin 5): Enable Pin. The on/off threshold voltage

is about VCC/2. When the input voltage is higher than

0.6 • VCC, the circuit is completely turned on. When the

input voltage is less than 0.4 • VCC, the circuit is turned off.

LO (Pin 6): Local Oscillator Input Pin.

VOUT (Pin 7): Output Pin.

BLOCK DIAGRA

VCC

VCC

1

8

7 VOUT

+

RF+ 2

RF– 3

RF

LIMITER

DET

DET

DET

DET

LIMITING

MIXER

LPF

IF

LIMITER

IF

• • • LIMITER

LO

BUFFER

6

LO

4

GND

ENABLE

5

EN

5504 BD

APPLICATIO S I FOR ATIO

The LT5504 consists of the following sections: RF/IF

limiters, limiting mixer, RF/IF detectors, LO buffer ampli-

fier, 3rd-order integrated low pass filter (LPF), output

interface and bias circuitry.

An RF signal ranging from 800MHz to 2.7GHz is detected

by the RF and IF detectors using a proprietary technique.

The down-converted IF signal is band limited by the on-

chip LPF, reducing broadband noise, and thus an ultrawide

dynamic range signal can be measured. The RF measuring

receiver is essentially a logarithmic voltage detector. The

measured output voltage is directly proportional to the RF

signal voltage. An internal temperature compensation

circuit results in a highly temperature-stable output volt-

age.

RF Limiter

The differential input impedance of the RF limiter is shown

in Figure 1. A 1:1 input transformer can be used to achieve

50Ω broadband matching with an 82Ω shunt resistor (R1)

at the inputs as shown in Figure 5.

The 1:1 RF input transformer can also be replaced with a

narrow band single-ended-to-differential conversion cir-

cuit using three discrete elements as shown in Figure 2.

Their nominal values are listed in Table 1. Due to the

parasitics of the PCB, these values may require adjust-

ment.

5504f

5

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