Datasheet
APPLICATION INFORMATION
WIDEBAND BUFFER OPERATION
V
CC
To V
CC
/2
BUF602
2k
Ω
50
Ω
0.1
µ
F
50
Ω
Load
V
OUT
V
CC
/2
0.1
µ
F
200
Ω
50
Ω
LOW-IMPEDANCE TRANSMISSION LINES
+
50
Ω
BUF602
50
Ω
V
IN
50
Ω
Source
V
OUT
50
Ω
Load
0.1
µ
F 4.7
µ
F
−
5V
+
0.1
µ
F 4.7
µ
F
+5V
Z =
O
L
T
C
T
(1)
BUF602
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...................................................................................................................................................... SBOS339B – OCTOBER 2005 – REVISED MAY 2008
single-supply operation of the BUF602 is to maintain
output signal swings within the usable voltage ranges.
The circuit of Figure 32 establishes an input midpoint
The BUF602 gives the exceptional AC performance
bias using the internal midpoint reference. The input
of a wideband buffer. Requiring only 5.8mA quiescent
signal is then AC-coupled into this midpoint voltage
current, the BUF602 will swing to within 1V of either
bias. Again, on a single +5V supply, the output
supply rail and deliver in excess of 60mA at room
voltage can swing to within 1V of either supply pin
temperature. This low output headroom requirement,
while delivering more than 60mA output current. A
along with supply voltage independent biasing, gives
demanding 100 Ω load to a midpoint bias is used in
remarkable single (+5V) supply operation. The
this characterization circuit.
BUF602 will deliver greater than 500MHz bandwidth
driving a 2V
PP
output into 100 Ω on a single +5V
supply.
Figure 31 shows the DC-coupled, dual power-supply
circuit configuration used as the basis of the ± 5V
Electrical and Typical Characteristics. For test
purposes, the input impedance is set to 50 Ω with a
resistor to ground and the output impedance is set to
50 Ω with a series output resistor. Voltage swings
reported in the specifications are taken directly at the
input and output pins while load powers (dBm) are
defined at a matched 50 Ω load. In addition to the
usual power-supply decoupling capacitors to ground,
a 0.01 µ F capacitor can be included between the two
power-supply pins. This optional added capacitor will
typically improve the 2nd-harmonic distortion
performance by 3dB to 6dB.
Figure 32. AC-Coupled, Single-Supply,
Specification and Test Circuit
The most important equations and technical basics of
transmission lines support the results found for the
various drive circuits presented here. An ideal
transmission medium with zero ohmic impedance
would have inductance and capacitance distributed
over the transmission cable. Both inductance and
capacitance detract from the transmission quality of a
line. Each input is connected with high-impedance to
the line as in a daisy-chain or loop-through
Figure 31. DC-Coupled, Bipolar Supply,
configuration, and each adds capacitance of at least
Specification and Test Circuit
a few picofarads. The typical transmission line
impedance (Z
O
) defines the line type. In Equation 1 ,
Figure 32 shows the AC-coupled, single-supply circuit
the impedance is calculated by the square root of line
configuration used as the basis of the +5V Electrical
inductance (L
T
) divided by line capacitance (C
T
):
and Typical Characteristics. Though not a rail-to-rail
design, the BUF602 requires minimal input and
output voltage headroom compared to other very
wideband buffers. It will deliver a 3V
PP
output swing
on a single +5V supply with greater than 400MHz
bandwidth. The key requirement of broadband
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