RF2713 datasheet(5/14 Pages) RFMD

5 / 14 page

7-51

RF2713

Rev A5 061016

Function

Description (Demodulator Configuration)

Interface Schematic

LO INPUT

High impedance, single-ended modulator LO input. The LO applied to

this pin is frequency divided by a factor of 2 and becomes the "Carrier".

For direct demodulation, the Carrier is equal in frequency to the center

of the input IF spectrum (except in the case of SSB/SC). The input

impedance is determined by an internal 500

Ω bias resistor to V

CC. An

external blocking capacitor should be provided if the pin is connected to

a device with DC present. Matching the input impedance is typically

achieved by adding a 51

Ω resistor to ground on the source side of the

AC coupling capacitor. For the LO input, maximum power transfer is not

critical. The internal LO switching circuits are controlled by the voltage,

not power, into the part. In cases where the LO source does not have

enough available voltage, a reactive match (voltage transformer) can

be used. The LO circuitry consists of a limiting amplifier followed by a

digital divider. The limiting amp ensures that the flip-flop type divider is

driven with a square wave over a wide range of input levels. Because

the flip-flop uses the rising and falling edges of the limiter output, the

quadrature accuracy of the Carrier supplied to the mixers is directly

related to the duty cycle, or equivalently to the even harmonic content,

of the input LO signal. In particular, care should be taken to ensure that

the 2xLO level input to this pin is at least 20dB below the LO level. Oth-

erwise, the LO input is not sensitive to the type of input wave form,

except for IF frequencies below ~2.5MHz, in which case the LO input

should be a square wave, in order to ensure proper triggering of the

flip-flops. IF frequencies below 100kHz are attainable if the LO is a

square wave and sufficiently large DC blocking capacitors are used.

VCC

Voltage supply for the entire device. This pin should be well bypassed

at all frequencies (IF, LO, Carrier, Baseband) that are present in the

part.

500

LO IN

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