_______________ Detailed Description
Bandwidth Control Circuitry
The MAX2470 features a logic-controlled bias circuit
which optimizes the performance for input frequencies
from 10MHz to 500MHz (HI/LO = V
CC
) and 10MHz to
200MHz (HI/LO = GND). Operating with HI/LO = GND
significantly reduces power consumption.
__________ Applications Information
Input Considerations
The MAX2470/MAX2471 offer high-impedance inputs,
ideal for low-distortion buffering of a VCO. For applica-
tions with discrete transistor-based oscillator designs,
simply AC-couple the oscillator directly to the inputs.
The buffer’s high input impedance results in minimal
loading on the oscillator. For still higher real input
impedance and reduced loading effects, match the
inputs with a shunt-L matching circuit followed by a
series blocking capacitor. For use with 50Ω VCO mod-
ules, terminate the buffer input(s) with a 50Ω shunt
resistor followed by a series-blocking capacitor. This
provides a very stable 50Ω termination and increases
reverse isolation. For those applications needing both
high gain and good input match, reactively match the
buffer inputs to 50Ω with simple two-element matching
circuits followed by a series blocking capacitor.
Output Considerations
The MAX2470 and MAX2471 incorporate fully differen-
tial output stages capable of driving an AC-coupled
100Ω differential load or two AC-coupled 50Ω single-
ended loads. This is ideal for applications that require
the oscillator to drive two application circuits (e.g. mixer
and PLL) simultaneously. The high output-to-output iso-
lation ensures minimal interaction between multiple
load circuits.
Layout and Power-Supply Bypassing
A properly designed PC board is essential to any RF/
microwave circuit. Be sure to use controlled impedance
lines on all high-frequency inputs and outputs. Bypass
the power supply with decoupling capacitors as close to
the V
CC
pins as possible. For long V
CC
lines (inductive), it
may be necessary to add additional decoupling capaci-
tors located further away from the device package.
Proper grounding of GND is essential. If the PC board
uses a topside RF ground, connect GND directly to it.
For a board where the ground plane is not on the com-
ponent side, the best technique is to connect GND to
the board with a plated through-hole (via) to the ground
plane close to the package.
MAX2470/MAX2471
10MHz to 500MHz VCO Buffer Amplifiers
with Differential Outputs
6 _______________________________________________________________________________________
Pin Description
Differential Noninverting Buffer Output. Broadband 50Ω output. AC coupling is required.
Do not DC couple to this pin.
OUT1
PIN
1
MAX2471MAX2470
NAME
2
RF Ground. Connect to the ground plane as close as possible to the IC to minimize
ground path inductance.
GND2
3
—
Bias and Bandwidth Control Input. Connect to V
CC
to set internal bias for higher band-
width operation (10MHz to 500MHz). Connect to GND to set internal bias for lower band-
width operation (10MHz to 200MHz) and to reduce overall current consumption.
HI/LO
4
Differential Inverting Buffer Output. Broadband 50Ω output. AC coupling is required. Do
not DC couple to this pin.
OUT
3
4
Differential Inverting Buffer Input. High impedance input to buffer amplifier. See
Setting
The Input Impedance
section.
IN
—
5
6 Supply Voltage Input. +2.7V < V
CC
< +5.5V.V
CC
6
Differential Noninverting Buffer Input. High impedance to buffer amplifier. See
Setting The
Input Impedance
section.
IN5
FUNCTION
