ICL8052ACDD INTERSIL [Intersil Corporation], ICL8052ACDD Datasheet - Page 13

• Manufacturer Part Number: ICL8052ACDD
• Description: 14-Bit/16-Bit, Microprocessor- Compatible, 2-Chip, A/D Converter
• Manufacturer: INTERSIL [Intersil Corporation]

Buffer Gain
At the end of the auto-zero interval, the instantaneous noise
voltage on the auto-zero capacitor is stored, and subtracts
from the input voltage while adding to the reference voltage
during the next cycle. The result is that this noise voltage
effectively is somewhat greater than the input noise voltage
of the buffer itself during integration. By introducing some
voltage gain into the buffer, the effect of the auto-zero noise
(referred to the input) can be reduced to the level of the
inherent buffer noise. This generally occurs with a buffer gain
of between 3 and 10. Further increase in buffer gain merely
increases the total offset to be handled by the auto-zero
loop, and reduces the available buffer and integrator swings,
without improving the noise performance of the system. The
circuit
ICL8068/ICL7104 is shown in Figure 7. With careful layout,
the circuit shown can achieve effective input noise voltages
Full scale V
Buffer Gain
R
C
C
C
V
Resolution
REF
INT
INT
AZ
REF
ICL7104-16 POL
ICL7104-14
ICL8052/8068 WITH
recommended
IN
TABLE 4. TYPICAL COMPONENT VALUES (V++ = +15V, V+ = 5V, V- = 5V, V- = -15V, f
HBEN
O/R
5k
for
POL
B16
300pF
10k
TABLE 3. THREE-STATE BYTE FORMATS AND ENABLE PINS
doing
B15
O/R
REF
OUT
ICL8052/ICL7104, ICL8068/ICL7104
FIGURE 7. ADDING BUFFER GAIN TO ICL8068
B14
B14
0.33
6
3
200
100
100
3.1
+15V
5
this
10
10
1
REF.
INT.
8
+BUF IN
B13
B13
7
-15V
MBEN
HBEN
with
1
B12
B12
ICL7104-16
13
10
-
BUFFER
BUF IN
10-50K
+
100k
-
A1
0.33
800
400
the
43
12
1
1
1
TO ICL7104
B11
B11
5-18
8068
BUF OUT
9
on the order of 1 to 2 V, allowing full 16-bit use with full scale
inputs of a low as 150mV. Note that at this level, thermoelec-
tric EMFs between PC boards, IC pins, etc., due to local
temperature changes can be very troublesome. For further
discussion, see Application Note AN030.
ICL8052 vs ICL8068
The ICL8052 offers significantly lower input leakage currents
than the ICL8068, and may be found preferable in systems
with high input impedances. However, the ICL8068 has
substantially lower noise voltage, and for systems where
system noise is a limiting factor, particularly in low signal
level conditions, will give better performance.
+INT IN
B10
B10
R
INT
CE/LD
B9
B9
4000
2000
11
12
0.33
200
INTEG.
61
-INT IN
1
1
1
+
-
C
A2
INT
-1.2V
B8
B8
14
INT OUT
COMP.
+
-
B7
B7
A3
100
0.1
6.1
10
47
10
50
2
1
B6
B6
ICL7104-14
COMP
OUT
-15V
+5V
CLOCK
B5
B5
LBEN
LBEN
= 200kHz)
B4
B4
4000
2000
180
244
0.1
1
1
1
B3
B3
B2
B2
UNIT
V/V
mV
mV
k
F
F
F
V
B1
B1