5 0 0 MHz t o 2 5 0 0 MHz
VCO Bu ffe r Am p lifie rs
V
(PIN 6)
V
(PIN 6)
CC
CC
INTERNAL
1.2V
REFERENCE
250Ω
1k
1.3pF
1k
BIAS
(PIN 3)
IN
(PIN 4)
GND
(PIN 2)
33Ω
Figure 3. BIAS Structure (MAX2473 only)
GND
(PIN 5)
the MAX2472/MAX2473 from the S parameter tables in
the Typical Operating Characteristics. Terminate the
Figure 1. Input Structure
buffer input with a shunt resistor “R
” such that
TERM
/MAX2473
R
RE[S ] = 50Ω, and use a series blocking
TERM
11
||
capacitor between the shunt resistor and the device
input. This provides a very stable 50Ω termination and
inc re a s e s re ve rs e is ola tion. For thos e a p p lic a tions
needing both high gain and good input match, reac-
tively match the buffer inputs to 50Ω with simple two-
element matching circuits. Figure 1 shows an equivalent
input circuit of the MAX2472/MAX2473 IN pin.
V
CC
(PIN 6)
2k
OUT
Ou t p u t Co n s id e ra t io n s
The MAX2472/MAX2473 outp uts a re c onfig ure d a s
open-collector output stages, allowing maximum flexi-
bility. To achieve maximum gain and output drive, reac-
tively match these outputs with a shunt inductor/choke
10Ω
to V
followed by a series capacitor (DC block). For
CC
applications not requiring high gain and output drive
(PLL prescaler), use a simple resistor to V followed
by a DC blocking capacitor. Figure 2 shows an equiva-
le nt c irc uit of the MAX2472/MAX2473 OUT p in(s ).
Figure 3 shows an equivalent circuit of the MAX2473
BIAS pin.
GND
(PIN 2)
CC
Figure 2. Output Structure
Ou t p u t Ma t c h in g Circ u it
Table 1 lists recommended values for lumped-element
output matching circuits at certain frequencies. For fre-
quencies other than those specified, use the parame-
ters given in the Typical Operating Characteristics.
Ap p lic a t io n s In fo rm a t io n
In p u t Co n s id e ra t io n s
The MAX2472/MAX2473 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 input; the
buffer’s high input impedance results in minimal load-
ing on the oscillator. For use with 50Ω VCO modules,
determine the approximate input impedance (S11) of
La yo u t a n d P o w e r-S u p p ly Byp a s s in g
A p rop e rly d e s ig ne d PC b oa rd is e s s e ntia l to a ny
RF/microwave circuit. Be sure to use controlled imped-
ance lines on all high-frequency inputs and outputs.
Bypass the power supply with decoupling capacitors
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