RF2713
Pin
13
Function Description (Demodulator Configuration)
Interface Schematic
High impedance, single-ended modulator LO input. The LO applied to
LO INPUT
VCC
VCC
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
500Ω
500Ω
impedance is determined by an internal 500Ω bias resistor to V . An
CC
LO IN
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 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 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.
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.
14
VCC
Rev A5 061016
7-51
RFMD [ RF MICRO DEVICES ]
