MAX4224 Maxim, MAX4224 Datasheet - Page 10

• Manufacturer Part Number: MAX4224
• Description: The MAX4223-MAX4228 current-feedback amplifiers combine ultra-high-speed performance, low distortion, and excellent video specifications with low-power operation
• Manufacturer: Maxim

1GHz, Low-Power, SOT23,
Current-Feedback Amplifiers with Shutdown
The MAX4223–MAX4228 are ultra-high-speed, low-
power, current-feedback amplifiers featuring -3dB
bandwidths up to 1GHz, 0.1dB gain flatness up to
300MHz, and very low differential gain and phase
errors of 0.01% and 0.02°, respectively. These devices
operate on dual ±5V or ±3V power supplies and
require only 6mA of supply current per amplifier. The
MAX4223/MAX4225/MAX4226 are optimized for
closed-loop gains of +1 (0dB) or more and have -3dB
bandwidths of 1GHz. The MAX4224/MAX4227/
MAX4228 are optimized for closed-loop gains of +2
(6dB) or more, and have -3dB bandwidths of 600MHz
(1.2GHz gain-bandwidth product).
The current-mode feedback topology of these ampli-
fiers allows them to achieve slew rates of up to
1700V/µs with corresponding large signal bandwidths
up to 330MHz. Each device in this family has an output
that is capable of driving a minimum of 60mA of output
current to ±2.5V.
Since the MAX4223–MAX4228 are current-feedback
amplifiers, their open-loop transfer function is
expressed as a transimpedance:
The frequency behavior of this open-loop transimped-
ance is similar to the open-loop gain of a voltage-feed-
back amplifier. That is, it has a large DC value and
decreases at approximately 6dB per octave.
Analyzing the current-feedback amplifier in a gain con-
figuration (Figure 1) yields the following transfer func-
tion:
At low gains, (G x R
tional voltage-feedback amplifiers, the closed-loop
bandwidth is essentially independent of the closed-
loop gain. Note also that at low frequencies, T
x R
10
_______________Detailed Description
where G
IN-
______________________________________________________________________________________
) + R
V
V
OUT
IN
F
], so that:
A
G x
V
V
OUT
V
IN
IN-
T S
1
Z
V
I
) << R
OUT
IN
R
R
G
G
F
.
or T
G x R
F
Theory of Operation
T S
. Therefore, unlike tradi-
1
Z
Z
R
R
IN
G
F
R
F
Z
>> [(G
The MAX4223/MAX4224/MAX4226/MAX4228 have a
shutdown mode that is activated by driving the SHDN
input low. When powered from ±5V supplies, the SHDN
input is compatible with TTL logic. Placing the amplifier
in shutdown mode reduces quiescent supply current to
350µA typical, and puts the amplifier output into a high-
impedance state (100kΩ typical). This feature allows
these devices to be used as multiplexers in wideband
systems. To implement the mux function, the outputs of
multiple amplifiers can be tied together, and only the
amplifier with the selected input will be enabled. All of
the other amplifiers will be placed in the low-power
shutdown mode, with their high output impedance pre-
senting very little load to the active amplifier output. For
gains of +2 or greater, the feedback network imped-
ance of all the amplifiers used in a mux application
must be considered when calculating the total load on
the active amplifier output.
The MAX4223–MAX4228 have an extremely high band-
width, and consequently require careful board layout,
including the possible use of constant-impedance
microstrip or stripline techniques.
Figure 1. Current-Feedback Amplifier
__________Applications Information
V
IN
R
G
Layout and Power-Supply Bypassing
IN+
IN-
Low-Power Shutdown Mode
+1
R
IN-
R
T
F
Z
+1
MAX4223
MAX4224
MAX4225
MAX4226
MAX4227
MAX4228
OUT