RF2713 datasheet(5/16 Pages) RFMD

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RF2713

Rev A5 DS061016

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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 VCC. 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

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 reac-

tive 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 mix-

ers 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. Otherwise, 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

VCC

RF2713 Datasheet(PDF) 5 Page - RF Micro Devices