adl5304 Analog Devices, Inc., adl5304 Datasheet - Page 23

• Manufacturer Part Number: adl5304
• Description: High Speed, 200 Db Range, Logarithmic Converter
• Manufacturer: Analog Devices, Inc.

Data Sheet
Table 4. VLOG Scaling Options
Option
Single-Supply Operation (VNEG = 0 V;
VSMx = DCBI = INPS = 1P5V)
1
2
3
4
5
6
7
8
Dual-Supply Operation (VNEG < −2 V;
VSMx = DCBI = INPS = Ground)
9
10
11
12
13
1
2
The default setups are noted in Table 4.
Other intercepts are achieved by injecting different currents
into the IDEN pin, for example, if I
Figure 52, the VLOG transfer function is simply shifted by one
decade to the right. One way of doing this is to put a precision
500 kΩ resistor between the 2VLT and IDEN pins in the single-
supply default setup. The intercept is moved up to 31.62 fA, and
all output voltages for a given I
that is, by 0.2 V at V
V
This is particularly useful if the slope is already as desired but
the desired intercept cannot be achieved with the on-chip
resistors. Only a shift toward the right makes sense because a
shift to the left requires excessively large resistors.
Default setup for single supply and VSMx = 1.5 V.
Default setup for dual supply and VSMx = ground.
1
2
LOG
Figure 52. Intercept Shifted One Decade Right via External Resistor,
= 1.3 V for I
PD
R
SHIELD
SHIELD
MNTR
500kΩ
VSM1
VSM2
VSM3
VSM4
NUM
INUM
IDEN
IREF
Reference Current I
LOG
= 100 nA.
2
3
4
5
6
7
8
. For example, the new I
100nA
17
1.5V
2VLT
MONITOR AND
(1.1× I
PD BIAS
30
1.5V
NUM
IMON
NUM
are lowered by one decade,
DEN
Q1
Q2
DEN
)
VNUM
VDEN
Q3
= 1 μA, as shown in
= 1 μA
Pin SCL1
VLOG
VLOG
VLOG
VLOG
VLOG
Open
Open
VLOG
VLOG
VLOG
VLOG
Open
Open
32
9
31
10
V
V
INNM
INDN
DEN
NUM
DEN
COMP
= 1 μA, and
TEMP
VREF
1.5V
26
1P5V
Pin SCL2
INMS
INMS
INMS
Open
Open
Open
VLOG
INMS
INMS
INMS
Open
Open
VLOG
I
LOG
Rev. 0 | Page 23 of 32
Pin SCL3
Open
VLOG
Ground
Ground
Open
VLOG
Open
2VLT
Open
VLOG
Open
VLOG
Open
Slope Inversion
Table 4 lists only those slopes that are positive because this is the
expected normal operation in measurement mode. The slopes can
be inverted by two methods. By using I
which case, the intercepts, I
the values shown in Table 4 around the 100 nA reference current.
For example, for the default setup with V
I
V
The second method is to simply swap the connections between
the VNUM and VDEN pins and the inputs to the temperature
compensation cell (INNM and INDN), as shown in Figure 53
(compare to Figure 52). This technique is particularly useful if
both negative log slope and adaptive photodiode biasing via
I
Z
MON
Y
= 3.162 fA, swapping INUM and IDEN connections result in
= −0.2 V/decade and I
are desired together.
Pin INPS
1P5V
1P5V
1P5V
1P5V
1P5V
1P5V
Ground
Ground
Ground
Ground
Ground
1P5V
1P5V
PD
R
SHIELD
SHIELD
MNTR
1.5V VREF
FROM
Figure 53. Simple Slope Inversion Method
VSM1
VSM2
VSM3
VSM4
INUM
IDEN
IREF
Pin INMS
SCL2
SCL2
SCL2
Open
Open
Open
Open
SCL2
SCL2
SCL2
Open
Open
Open
2
3
4
5
6
7
8
100nA
Z
Z
, are at larger currents mirrored from
= 3.162 A.
IMON
MONITOR AND
(1.1× I
PD BIAS
30
V
0.2
0.15
0.2
0.4
0.4
0.6
0.8
0.2
0.2
0.15
0.4
0.6
0.8
Y
NUM
(V/dec)
Q1
Q2
NUM
)
VNUM
VDEN
Q3
= I
Y
= 0.2 V/decade and
32
9
REF
I
3.16 f
0.01 f
0.01 f
56.2 f
17.8 p
316 p
1.33 n
21.6 f
100 n
100 n
100 n
100 n
100 n
= 100 nA, in
Z
(A)
31
10
V
V
INDN
ADL5304
INNM
NUM
DEN
COMP
TEMP
V
1.5
1.5
2.0
2.5
1.5
1.5
1.5
1.333
0
0
0
0
0
OFS
(V)