iC-TW2 8-BIT SIN/COS INTERPOLATION IC
WITH INTEGRATED EEPROM
Rev D3, Page 11/30
INPUT STAGE
OFSA(5:0)
Addr. 0x08; bit 5:0
Addr. 0x09; bit 5:0
R/W
R/W
A programmable gain amplifier (PGA) with output re-
ferred offset adjustment is used as input stage, shown
OFSB(5:0)
Code
Function, defaults to eeprom setting
in Figure 3. The coarse gain is common for both
channel A and B and is programmed through regis-
ter GC(2:0). Table 5 shows the required gain setting
for a given input signal amplitude (peak to peak, differ-
ential). Fine tuning gain is applied individually to chan-
nel A and B by programming registers GFA(1:0) and
GFB(1:0) respectively.
111111
111110
100001
100000
000000
000001
011110
011111
maximum negative adjust: -403 mV
-390 mV
-13 mV
no correction
no correction
13 mV
390 mV
maximum positive adjust: 403 mV
GC(2:0)
Code
000
Addr. 0x07; bit 2:0
Function, defaults to eeprom setting
1.5 V - 800 mV
R/W
Table 7: Offset control of channel A/B
001
800 mV - 400 mV
400 mV - 200 mV
200 mV - 100 mV
100 mV - 50 mV
Consider Table 8 regarding the relationship between
input signal peak-peak differential amplitude, amplifier
gain setting and resulting offset correction range.
010
011
100
101
50 mV - 25 mV
Input amplifier gain and offset
110
25 mV - 10 mV
Input signal range
Register
GC(2:0)
Input
referred
Input
referred
111
not defined
offset step offset
size
range
Table 5: Coarse gain control of channel A/B
800 mV - 1.5 V
400 mV - 800 mV
200 mV - 400 mV
100 mV - 200 mV
50 mV - 100 mV
25 mV - 50 mV
10 mV - 25 mV
0
1
2
3
4
5
6
26 mV
±806 mV
±403 mV
±202 mV
±101 mV
±50 mV
±25 mV
±12.6 mV
13 mV
6.5 mV
3.25 mV
1.63 mV
0.81 mV
0.41 mV
GFA(1:0)
Addr. 0x07; bit 4:3
R/W
R/W
GFB(1:0)
Code
00
Addr. 0x07; bit 6:5
Function, defaults to eeprom setting
0 dB
01
0.7 dB
1.4 dB
2.1 dB
10
Table 8: Input amplifier gain and offset
11
Input
Table 6: Fine gain control of channel A/B
amplifier
OFSB(5:0)
GFB(1:0)
+
-
PINB
NINB
Xb
+
Offset adjustment is provided at the output of the input
amplifier. It is individually programmed through regis-
ter OFSA(5:0) and OFSB(5:0). Adjustment is made in
steps of 13 mV and the corresponding register values
are sign magnitude encoded. Input referred offset be-
comes gain dependent and is defined as follows:
GC(2:0)
to interpolation
engine
+
-
PINA
NINA
Xa
+
GFA(1:0)
OFSA(5:0)
13 mV ∗ OFSA(5 : 0)
=
Figure 3: Input stage
OFSAinput_referred
GC(2 : 0)
ICHAUS [ IC-HAUS GMBH ]
