AD8304ARUZ-RL7 Analog Devices Inc, AD8304ARUZ-RL7 Datasheet - Page 14

• Manufacturer Part Number: AD8304ARUZ-RL7
• Description: IC,Level Detector,TSSOP,14PIN,PLASTIC
• Manufacturer: Analog Devices Inc
• Type: Logarithmic Converterr

Specifications of AD8304ARUZ-RL7

• Design Resources: Interfacing ADL5315 to Translinear Logarithmic Amplifier (CN0056) Interfacing ADL5317 High Side Current Mirror to a Translinear Logarithmic Amplifier in an Avalanche Photodiode Power Detector
• Applications: Fiber Optics
• Mounting Type: Surface Mount
• Package / Case: 14-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD8304
ACOM Pin, and does not normally go negative with regard to this
pin, but is free to do so. Therefore, a resistor from VLOG to the
negative supply can lower V
accurate method for repositioning the intercept is described below.
Figure 11. Log Conformance (Linearity) vs. I
Various Negative Supplies
–0.5
–1.0
–1.5
–2.0
2.0
1.5
1.0
0.5
0
100p
WITH INTERCEPT ADJUST
1n
WITHOUT INTERCEPT ADJUST
10n
I1
IPD
100n
LOG
IN
, thus raising the intercept. A more
INPUT – A
I1
C1
E1
V1
Q1
I2
Q2
I3
Q3
.MODEL
E2
E3
E4
V2
R1
C2
R2
RL
C1
1
V1
V
0
IN
2
1
IN
0
3
0
4
NPN
5
6
7
8
8
9
9
VLOG
10
Q1
+
1
V
IN
0
0
0
2
3
3
4
4
NPN
0
0
0
7
9
0
VLOG
0
NEG
100
V
NEG
= –0.5
3k
DC
1.0N
IN
0.5
0
1
0
316.2
0
POLY (2)
POLY (2)
6
0.8
100
163P
4.9K
1000K
= –3
V
1m
NEG
Figure 12. Basic Macromodel
2
= 0
I1
3
PD
Q2
1 A
1
NPN
NPN
NPN
2 3 1 0 0, 0, 0, 0, 1
4 3 7 0 0, 0, 0, 0, 1
5
10m
for
I2
4
Q3
3K
100K
–14–
E2
APPLICATIONS
The AD8304 incorporates features that improve its usefulness in
both fiber optic supervisory applications and in more general ones.
To aid in the exploration of these possibilities, a SPICE macro-
model is provided and a versatile evaluation board is available.
The macromodel is shown in generalized schematic form (and thus
is independent of variations in SPICE programs) in Figure 12.
Q1, QM, and Q2 (here made equal in size) correspond to the
identical transistors in Figure 1. The model parameters for these
transistors are not critical; the default model provided in SPICE
libraries will be satisfactory. However, the AD8304 employs
compensation techniques to reduce errors caused by junction
resistances (notably, RB and RE) at high input currents. There-
fore, it is advisable to set these to zero. While this will not model
the AD8304 precisely, it is safer than using possibly high default
values for these parameters. The low current model parameters
may also need consideration. Note that no attempt is made to
capture either dynamic behavior or the effects of temperature in this
simple macromodel; scaling is correct for 27°C.
E3
6
5
100k
E4
7
V2 R1
V
+
C2
R2
RL
VLOG
REV. A