Datasheet MAX2472, MAX2473 (Analog Devices) - 10

500MHz to 2500MHz VCO Buffer Amplifiers
VCC VCC (PIN 6) (PIN 6) INTERNAL 1.2V 250Ω REFERENCE 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
MAX2472/MAX2473
Figure 1. Input Structure buffer input with a shunt resistor “RTERM” such that RTERM || RE[S11] = 50Ω, and use a series blocking capacitor between the shunt resistor and the device VCC (PIN 6) input. This provides a very stable 50Ω termination and increases reverse isolation. For those applications needing both high gain and good input match, reac- tively match the buffer inputs to 50Ω with simple two- 2k element matching circuits. Figure 1 shows an equivalent OUT input circuit of the MAX2472/MAX2473 IN pin.
Output Considerations
The MAX2472/MAX2473 outputs are configured as open-collector output stages, allowing maximum flexi- bility. To achieve maximum gain and output drive, reac- 10Ω tively match these outputs with a shunt inductor/choke to VCC followed by a series capacitor (DC block). For applications not requiring high gain and output drive GND (PLL prescaler), use a simple resistor to VCC followed (PIN 2) by a DC blocking capacitor. Figure 2 shows an equiva- lent circuit of the MAX2472/MAX2473 OUT pin(s). Figure 2. Output Structure Figure 3 shows an equivalent circuit of the MAX2473 BIAS pin.
Applications Information Output Matching Circuit
Table 1 lists recommended values for lumped-element
Input Considerations
output matching circuits at certain frequencies. For fre- The MAX2472/MAX2473 offer high-impedance inputs quencies other than those specified, use the parame- ideal for low-distortion buffering of a VCO. For applica- ters given in the Typical Operating Characteristics. tions with discrete transistor-based oscillator designs,
Layout and Power-Supply Bypassing
simply AC-couple the oscillator directly to the input; the buffer’s high input impedance results in minimal load- A properly designed PC board is essential to any ing on the oscillator. For use with 50Ω VCO modules, RF/microwave circuit. Be sure to use controlled imped- determine the approximate input impedance (S11) of ance lines on all high-frequency inputs and outputs. Bypass the power supply with decoupling capacitors
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