LTC2257-14_15 Datasheet, PDF (18/34 Pages) Linear Technology – 14-Bit, 65/40/25Msps Ultralow Power 1.8V ADCs

LTC2258-14
LTC2257-14/LTC2256-14
Applications Information
CONVERTER OPERATION
The LTC2258-14/LTC2257-14/LTC2256-14 are low power
14-bit 65Msps/40Msps/25Msps A/D converters that are
powered by a single 1.8V supply. The analog inputs should
be driven differentially. The encode input can be driven
differentially, or single ended for lower power consump-
tion. The digital outputs can be CMOS, double data rate
CMOS (to halve the number of output lines), or double
data rate LVDS (to reduce digital noise in the system.)
Many additional features can be chosen by programming
the mode control registers through a serial SPI port. See
the Serial Programming Mode section.
ANALOG INPUT
The analog input is a differential CMOS sample-and-hold
circuit (Figure 2). The inputs should be driven differentially
around a common mode voltage set by the V_CM output
pin, which is nominally V_DD/2. For the 2V input range,
the inputs should swing from V_CM – 0.5V to V_CM + 0.5V.
There should be 180° phase difference between the inputs.
LTC2258-14
V_DD
10Ω
A_IN+
V_DD
10Ω
A_IN–
V_DD
C_PARASITIC
1.8pF
C_PARASITIC
1.8pF
R_ON
C_SAMPLE
3.5pF
25Ω
C_SAMPLE
R_{ON 3.5pF}
25Ω
ENC⁺
ENC^–
1.2V
10k
10k
1.2V
225814 F02
Figure 2. Equivalent Input Circuit
18
For more information www.linear.com/LTC2258-14
225814fc