MAX1191 Datasheet, PDF (15/27 Pages) Maxim Integrated Products – Ultra-Low-Power, 7.5Msps, Dual 8-Bit ADC

Ultra-Low-Power, 7.5Msps, Dual 8-Bit ADC
INTERNAL
BIAS
S2a
S4a
INA+
C2a
S4c
S1
COM
S5a
C1a
S3a
OUT
INA-
S4b
C2b
OUT
C1b
S2b
INTERNAL
BIAS
INTERNAL
BIAS
S2a
S3b
S5b
COM
COM
S5a
C1a
S3a
HOLD
HOLD
CLK
TRACK
TRACK
INTERNAL
NONOVERLAPPING
CLOCK SIGNALS
S4a
INB+
C2a
S4c
S1
INB-
S4b
C2b
C1b
OUT
MAX1191
OUT
S2b
INTERNAL
BIAS
S3b
S5b
COM
Figure 3. Internal T/H Circuits
Input Track-and-Hold (T/H) Circuits
Figure 3 displays a simplified functional diagram of the
input T/H circuits. In track mode, switches S1, S2a,
S2b, S4a, S4b, S5a, and S5b are closed. The fully dif-
ferential circuits sample the input signals onto the two
capacitors (C2a and C2b) through switches S4a and
S4b. S2a and S2b set the common mode for the ampli-
fier input, and open simultaneously with S1, sampling
the input waveform. Switches S4a, S4b, S5a, and S5b
are then opened before switches S3a and S3b connect
capacitors C1a and C1b to the output of the amplifier
and switch S4c is closed. The resulting differential volt-
ages are held on capacitors C2a and C2b. The ampli-
fiers charge capacitors C1a and C1b to the same
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