
Operation
The CLC532 is a 2:1 analog multiplexer with high-impedance
buffered inputs, and a low-impedance, low-distortion, output
stage. The CLC532 employs a closed-loop design, which
dramatically improves accuracy. The channel SELECT control
(Figure 1) determines which of the two inputs (IN
or IN
) is
present at the OUTPUT. Beyond the basic multiplexer function,
the CLC532 offers compatibility with either TTL or ECL logic
families, as well as adjustable bandwidth.
R
L
R
IN
R
IN
5
IN
B
8
10
6
9
IN
A
4
3
2
1
7
13
14
V
OUT
12
CHANNEL A
CHANNEL B
CHANNEL
SELECT
DGND
-5.2V
0.1
μ
F
C
COMP2
C
COMP1
+5V
CLC532
D
REF
11
0.1
μ
F
+6.8
μ
F
+6.8
μ
F
Figure 1: Standard CLC532 Circuit Configuration
Digital Interface and Channel SELECT
The CLC532 functions with ECL, TTL and CMOS logic families.
D
controls logic compatibility. In normal operation, D
is left
floating, and the channel SELECT responds to ECL level signals,
Figure 2. For TTL or CMOS level SELECT inputs (Figure 3), D
should be tied to +5V (the CLC532 incorporates an internal
2300
series isolation resistor for the D
input). For TTL or
CMOS operation, the channel SELECT requires a resistor input
network to prevent saturation of the channel select circuitry.
Without this input network, channel SELECT logic levels above
3V will cause internal junction saturation and slow switching
speeds.
ECL GATE
SELECT
A
/
B
50
50
-2V
D
REF
(NC)
7
SELECT
6
CLC532
-5.2V
TGate
SETo
130
81
Output Termination
R1
R2
Figure 2: ECL Level Channel SELECT Configuration
+5V
SELECT
A
/
B
7
D
REF
+5V
6
CLC532
TTL
3.6k
510
R3
R2
R1
R2
R3
R1
Figure 3: TTL/CMOS Level Channel SELECT Configuration
Compensation
The CLC532 incorporates compensation nodes that allow both
its bandwidth and its settling time/slew rate to be adjusted.
Bandwidth and settling time/slew adjustments are linked,
meaning that lowering the bandwidth also lowers slew rate
and lengthens settling time. Proper adjustment (compensation)
is necessary to optimize system performance. Time Domain
applications should generally be optimized for lowest RMS
noise at the CLC532 output, while maintaining settling time and
slew rates at adequate levels to meet system needs. Frequency
Domain applications should generally be optimized for maximally
flat frequency response.
Figure 4 below describes the basic relationship between
bandwidth and R
for various values of load capacitance, C
L
,
where C
COMP
= 10pF.
0.01%
0.05%
Rs
Ts
1k
R
s
C
L
2V Output Step
C
L
(pF)
R
s
(
)
S
s
(
1
100
1000
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Figure 4: Settling Time and R
S
vs. C
L
Figure 5 shows the resulting changes in bandwidth and slew rate
for increasing values of C
. The RMS noise at the CLC532
output can be approximated as:
OUTPUT
NOISERMS
= (n
V
)(
√
1.57*BW
-3dB
)
where... n
= input spot noise voltage;
BW
-3dB
= Bandwidth is from figure 5.
S
μ
s
1
10
100
C
comp
(pF)
200
180
160
140
120
100
80
60
40
20
0
-3dB Bandwidth
Slew Rate
200
180
160
140
120
100
80
60
40
20
Figure 5: C
COMP
for Maximally Flat Frequency Response
Applications Information
http://www.national.com
6