an1184

ISL59444EVAL1 Evaluation Board User’s Guide
®
Application Note
April 19, 2005
AN1184.0
Introduction
High Frequency Layout Considerations
The ISL59444EVAL1 evaluation board contains all the
circuitry needed to characterize critical performance
parameters of the ISL59444 single 4:1 MUX-amplifier, over a
variety of applications.
At frequencies of 500MHz and higher, circuit board layout
may limit performance. The following layout guidelines are
implemented on the evaluation board:
The ISL59444 is a single-output 4:1 MUX-amps with a unitygain bandwidth of 1GHz. The device contains logic inputs for
channel selection (S0, S1) three-state output control (HIZ)
that allows individual selection of MUX amps that share a
common video output line. Latches LE1 and LE2 provide
synchronous switching of the channel select logic to the
output.
The evaluation board circuit and layout is optimized for
either 50Ω or 75Ω terminations, and implements a basic
single 4:1 video MUX-amp. The board is supplied with 75Ω
input signal terminations and a 75Ω back-termination
resistor on each of the 3 outputs, making it suitable for
driving video cable. The user has the option of replacing the
75Ω resistors with 50Ω resistors for other applications. The
control lines contain 50Ω resistors to match the 50Ω output
impedance of high speed pulse generators. Control line
termination resistors are recommended for rise and fall times
under 10ns to minimize unwanted transients. If DC is used
for the control logic, the resistors may be removed; or the
applied DC voltage can be reduced to 2.5V to reduce the
dissipation in the termination resistor.
The layout contains component options to include an output
series resistor (RS) followed by a parallel resistor (RL)
capacitor (CL) network to ground. This option allows the user
to select several different output configurations. Examples
are shown in Figures 3A, 3B, and 3C. The evaluation board
is supplied with the 75Ω back termination resistors shown in
Figure 3C.
• Signal I/O lines are the same lengths and widths to match
propagation delay and trace parasitics.
• No series connected vias are used in signal I/O lines, as
they can add unwanted inductance.
• Signal trace lengths are minimized to reduce transmission
line effects and the need for strip-line tuning of the signal
traces.
• High frequency decoupling caps are places as close to the
device power supply pin as possible - without series vias
between the capacitor and the device pin.
Power Sequencing
Proper power supply sequencing is -V first, then +V. In
addition, the +V and -V supply pin voltage rate-of-rise must
be limited to ±1V/µs or less. The evaluation board contains
parallel-connected low VON Schottky diodes on each supply
terminal to minimize the risk of latch up due to incorrect
sequencing. In addition, extra 10µF decoupling capacitors
are added to each supply to aid in reducing the applied
voltage rate-of-rise.
Reference Documents
• ISL59444 Data Sheet, FN7451
EN0
DL Q
C
DL Q
C
EN1
DL Q
C
DL Q
C
EN2
DL Q
S0
DECODE
S1
HIZ
Amplifier Performance and Output
Configurations
EN3
The ISL59444 output amplifier is sensitive to capacitance at
the output. For best AC performance, a series output resistor
is required to reduce excessive gain peaking, particularly
when long PB board traces are used. The output amplifier is
ideally suited for driving high impedance high speed
selectable-gain buffers when gain compensation is needed.
GBW decreases slightly at the lower output load
impedances typical of back-terminated cable driving
applications. Reference data sheets for additional
performance data.
LE1
LE2
C
DL Q
C
DL Q
C
DL Q
C
IN0
OUT
IN1
IN2
IN3
100kΩ
100kΩ
FIGURE 1. ISL59444 FUNCTIONAL BLOCK DIAGRAM
LE1
LE2
S0, S1, HIZ
OUT
CHX
CHX
CHY
CHZ
CHY
CHX
CHX
CHZ
CHZ
FIGURE 2. ISL59444 TIMING DIAGRAM
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Application Note 1184
TABLE 1. LOGIC TABLE
ISL59444
VIN
50Ω
OR
75Ω
S0
S1
LE1/LE2
HIZ
OUT
0
0
0
0
IN0
1
0
0
0
IN1
0
1
0
0
IN2
1
1
0
0
IN3
-
-
0
1
High Z
-
-
Timing Diagram
0
Timing Diagram
ISL59444
RS, 0Ω
VIN
*Cb2
~3pF
Cb1
~0.5pF
500Ω
* Cb1, Cb2 are approximate PCB trace capacitances.
50Ω
OR
75Ω
FIGURE 3B. TEST CIRCUIT FOR 50Ω OR 75Ω TERMINATIONS
ISL59444
50Ω
OR
75Ω
50Ω
OR
75Ω
* Cb1 is approximate PCB trace capacitance.
FIGURE 3A. TEST CIRCUIT WITH OPTIMAL OUTPUT LOAD
VIN
475Ω
Cb1
RL
~0.5pF
50Ω
OR
75Ω
RL
TEST
EQUIPMENT
RS
RS
50Ω OR 75Ω
Cb1
~0.5pF
TEST
EQUIPMENT
50Ω
OR
75Ω
* Cb1 is approximate PCB trace capacitance.
FIGURE 3C. BACK-TERMINATED TEST CIRCUIT FOR CABLE APPLICATION
ISL59444EVAL1 Top View
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Application Note 1184
ISL59444EVAL1 Schematic Diagram
ISL59444
IN0
R9
75Ω
IN1
R2
75Ω
1 IN0
V+ 16
2 GND
S0 15
3 IN1
S1 14
HIZ 13
4 GND
IN2
OUT 12
5 IN2
R10
75Ω
IN3
R11
75Ω
JS0
S0
JS1
R19 - 49.9Ω
S1
JHIZ
R18 - 49.9Ω
HIZ
R12 - 49.9Ω
OUT
RS - 75Ω
6 GND
LE2 11
7 IN3
LE1 10
V- 8
8 GND
R21
C10
R6 - 49.9Ω
LE2
R5 - 49.9Ω
LE1
D1
C3
10µF
C2
0.1µF
C1
10nF
C7
1nF
+
C6
10µF
D2
+
GND
V-
C5
0.1µF
C4
10nF
C8
1nF
V+
ISL59444EVAL1 Components Parts List
DEVICE #
DESCRIPTION
COMMENTS
C7, C8
CAP, SMD, 0603, 1000pF, 25V, 10%, X7R
Power Supply Decoupling
C1, C4
CAP, SMD, 0603, 0.01µF, 25V, 10%, X7R
Power Supply Decoupling
C2, C5
CAP, SMD, 0603, 0.1µF, 25V, 10%, X7R
Power Supply Decoupling
C3, C6
CAP, SMD, 0805, 10µF, 6.3V, 10%, X5R
Power Supply Decoupling
D1, D2
Diode-Schottky, 2 Pin, 45V, 7.5A
MBR0550T (Motorola) Reverse Polarity Protection
R2, R9, R10, R11, RS
Resistor, SMD, 0603, 75Ω, 1/10W, 1%
Signal Input/output Termination
R5, R6, R12, R18, R19
Resistor, SMD, 0603, 49.9Ω, 1/16W, 1%
Logic Input Termination
C10
Resistor, SMD, 0603
Optional, not populated
R21
Resistor, SMD, 0603
Optional, not populated
U1
ISL59444 - 1GHz Multiplexing Amplifier, 16P, QSOP
Device Under Test
Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to
verify that the Application Note or Technical Brief is current before proceeding.
For information regarding Intersil Corporation and its products, see www.intersil.com
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