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RF2485

VHF QUADRATURE MODULATOR

RF Micro Devices 

Preliminary

RF2485

Pin Function Description

Interface Schematic

1

VDD2

Power supply for the RF Output amplifier. An external RF bypass

capacitor is needed. The trace length between the pin and the bypass

capacitor should be minimized. The ground side of the capacitor should

connect immediately to the ground plane.

2

VDD1

Power supply for all other circuits. An external RF bypass capacitor is

needed.

3

NC

No connection.

4

I SIG

Baseband input to the I mixer. This pin is DC coupled. Maximum output

I REF

I SIG

power is obtained when the input signal has a peak to peak amplitude

of 5V. The DC level supplied to this pin should be 2.5±0.5V. The SIG

and REF inputs are inputs of a differential amplifier. Therefore the REF

and SIG inputs are interchangeable. If swapping the I SIG and I REF

pins, the Q SIG and Q REF also need to be swapped to maintain the

correct phase. It is also possible to drive the SIG and REF inputs in a

balanced mode. This will increase the gain.

5

5

I REF

Reference voltage for the I mixer. This voltage should be the same as See pin 4.

the DC voltage supplied to the I SIG pin. To obtain a carrier suppres-

sion of better than 40dB it may be tuned ±0.15V (relative to the I SIG

DC voltage). Without tuning, it will typically be better than 25dB.

6

Q REF

Reference voltage for the Q mixer. This voltage should be the same as Same as pin 3.

the DC voltage supplied to the Q SIG pin. To obtain a carrier suppres-

sion of better than 40dB it may be tuned ±0.15V (relative to the Q SIG

DC voltage). Without tuning, it will typically be better than 25dB. The

SIG and REF inputs are inputs of a differential amplifier. Therefore the

REF and SIG inputs are interchangeable. If swapping the I SIG and I

REF pins, Q SIG and Q REF also need to be swapped to maintain cor-

rect phase. It is also possible to drive the SIG and REF inputs in a bal-

anced mode. This will increase the gain.

7

Q SIG

Baseband input to the Q mixer. This pin is DC coupled. Maximum out- Same as pin 4.

put power is obtained when the input signal has a peak to peak ampli-

tude of 5V. The DC level supplied to this pin should be 2.5±0.5V.

8

LO IN

The input of the phase shifting network. This high impedance input can

be matched with an external 56Ω termination resistor. This pin is inter-

LO IN

nally connected to ground through a 4kΩ resistor. Putting a DC voltage

on this pin is not recommended. However, connecting this pin to

ground, e.g., through a shunt inductor, is allowed.

9

PHASE This pin allows to adjust the phase of the I/Q signals. However, the con-

trol is very sensitive and hard to control. Control voltage change for a

few degrees adjustment is in the order of 10mV. Device to device and

temperature variation are not characterized. Therefore it is not recom-

mended to use this pin; leave it not connected. Do NOT connect to

ground.For compensating large errors in the I/Q signals supplied to the

device or in control loops this pin may prove useful.

10

GND1

Ground connection of the LO phase shift network. This pin should be

connected directly to the ground plane.

11

GND

Ground connection for other circuits. Keep traces short and connect to

ground plane immediately.

12

GND

Same as pin 11.

13

GND2

Ground connection for the RF output stage. A good ground connection

is especially important at this pin to avoid interference with other cir-

cuits.

PHASE

Rev A3 010820

5-57

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