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RF2713

QUADRATURE MODULATOR/DEMODULATOR

RF Micro Devices 

RF2713

Pin Function Description (Demodulator Configuration)

Interface Schematic

13

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

VCC

VCC

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

500 Ω

500 Ω

determined by an internal 500Ω bias resistor to VCC. An external blocking

LO IN

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

51Ω 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.

14

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.

Rev A5 DS061016

7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical

support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.

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