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Detailed Description
The MAX4214/MAX4215/MAX4217/MAX4219/MAX4222
are single-supply, rail-to-rail output, voltage-feedback,
closed-loop buffers that employ current-feedback tech-
niques to achieve 600V/µs slew rates and 230MHz
bandwidths. These buffers use internal 500Ω resistors
to provide a preset closed-loop gain of 2V/V in the non-
inverting configuration or -1V/V in the inverting configu-
ration. Excellent harmonic distortion and differential
gain/phase performance make them an ideal choice for
a wide variety of video and RF signal-processing appli-
cations.
Local feedback around the buffer’s output stage
ensures low output impedance, which reduces gain
sensitivity to load variations. This feedback also pro-
duces demand-driven current bias to the output tran-
sistors for ±120mA drive capability, while constraining
total supply current to less than 7mA.
___________Applications Information
Power Supplies
These devices operate from a single 3.15V to 11V
power supply or from dual supplies of ±1.575V to
±5.5V. For single-supply operation, bypass the V
CC
pin
to ground with a 0.1µF capacitor as close to the pin as
possible. If operating with dual supplies, bypass each
supply with a 0.1µF capacitor.
Selecting Gain Configuration
Each buffer in the MAX4214 family can be configured
for a voltage gain of 2V/V or -1V/V. For a gain of 2V/V,
ground the inverting terminal. Use the noninverting ter-
minal as the signal input of the buffer (Figure 1a).
Grounding the noninverting terminal and using the
inverting terminal as the signal input configures the
buffer for a gain of -1V/V (Figure 1b).
Since the inverting input exhibits a 500Ω input imped-
ance, terminate the input with a 56Ω resistor when con-
figured for an inverting gain in 50Ω applications
(terminate with 88Ω in 75Ω applications). Terminate the
input with a 49.9Ω resistor in the noninverting case.
Output terminating resistors should directly match
cable impedances in either configuration.
Layout Techniques
Maxim recommends using microstrip and stripline tech-
niques to obtain full bandwidth. To ensure the PC
board does not degrade the buffer’s performance,
design it for a frequency greater than 1GHz. Pay care-
ful attention to inputs and outputs to avoid large para-
sitic capacitance. Whether or not you use a constant-
impedance board, observe the following guidelines
when designing the board:
• Don’t use wire-wrapped boards. They are too induc-
tive.
• Don’t use IC sockets. They increase parasitic capac-
itance and inductance.
• Use surface-mount instead of through-hole compo-
nents for better high-frequency performance.
• Use a PC board with at least two layers; it should be
as free from voids as possible.
• Keep signal lines as short and as straight as possi-
ble. Do not make 90° turns; round all corners.
Input Voltage Range and Output Swing
The MAX4214 family’s input range extends from
(V
EE
- 100mV) to (V
CC
- 2.25V). Input ground sensing
increases the dynamic range for single-supply applica-
tions. The outputs drive a 2kΩ load to within 60mV of
the power-supply rails. With smaller resistive loads, the
output swing is reduced as shown in the Electrical
Characteristics and Typical Operating Characteristics.
MAX4214/MAX4215/MAX4217/MAX4219/MAX4222
High-Speed, Single-Supply, Gain of 2,
Closed-Loop, Rail-to-Rail Buffers with Enable
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