Datasheet

www.ti.com
APPLICATION INFORMATION
THEORY OF OPERATION
ANALOG INPUT
Resr
200 W
Lpkg
nH»1
25 W
Sampling
Capacitor
Csamp
4.0pF
INP
INM
Cbond
pF»1
50 W
Cpar1
0.8pF
Cpar2
1pF
Ron
15 W
Ron
10 W
Ron
15 W
Cpar2
1pF
50 W
3.2pF
Lpkg
1nH»
25 W
Cbond
pF»1
Resr
200 W
Csamp
4.0pF
Sampling
Capacitor
Sampling
Switch
Sampling
Switch
RCRFilter
ADS6145, ADS6144
ADS6143, ADS6142
SLWS198B – JULY 2007 – REVISED MARCH 2008
The ADS614X devices are a family of low power, 14-bit pipeline ADCs in a CMOS process with up to a 125
MSPS sampling frequencies. These devices are based on switched capacitor technology and run off a single
3.3-V supply. The conversion process is initiated by the rising edge of the external input clock. Once the signal is
captured by the input sample and hold, the input sample is sequentially converted by a series of lower resolution
stages, with the outputs combined in a digital correction logic block. At every clock edge, the sample propagates
through the pipeline resulting in a data latency of 9 clock cycles. The output is available as 14-bit data, in DDR
LVDS or CMOS and coded in either straight offset binary or binary 2s complement format.
The analog input consists of a switched-capacitor based differential sample and hold architecture, shown in
Figure 92 .
This differential topology results in good ac-performance even for high input frequencies at high sampling rates.
The INP and INM pins have to be externally biased around a common-mode voltage of 1.5 V available on the
VCM pin. For a full-scale differential input, each input pin (INP, INM) has to swing symmetrically between VCM +
0.5 V and VCM – 0.5 V, resulting in a 2V
PP
differential input swing. The maximum swing is determined by the
internal reference voltages REFP (2.5 V nominal) and REFM (0.5 V, nominal).
Figure 92. Input Stage
The input sampling circuit has a high 3dB bandwidth that extends up to 450 MHz (measured from the input pins
to the voltage across the sampling capacitors).
Copyright © 2007 – 2008, Texas Instruments Incorporated Submit Documentation Feedback 41
Product Folder Link(s): ADS6145, ADS6144 ADS6143, ADS6142