Datasheet

INP
INM
25 W
25 W
RCR Filter
50 W
50 W
3.2 pF
C
1pF
par2
C
1pF
par2
L
3nH
pkg
L
3nH
pkg
C
2pF
bond
C
2pF
bond
R
200
esr
W
R
200
esr
W
C
0.8 pF
par1
Sampling
Switch
Sampling
Switch
Sampling
Capacitor
Sampling
Capacitor
R
15
on
W
R
15
on
W
R
10
on
W
C
4.0 pF
samp
C
4.0 pF
samp
S0237-01
ADS6445, ADS6444
ADS6443, ADS6442
SLAS531B –MAY 2007–REVISED DECEMBER 2009 www.ti.com
APPLICATION INFORMATION
THEORY OF OPERATION
The ADS6445/ADS6444/ADS6443/ADS6442 (ADS644X) is a family of quad channel, 14-bit pipeline ADC based
on switched capacitor architecture in CMOS technology.
The conversion is initiated simultaneously by all the four channels at the rising edge of the external input clock.
After the input signals are captured by the sample and hold circuit of each channel, the samples are sequentially
converted by a series of low resolution stages. The stage outputs are combined in a digital correction logic block
to form the final 14-bit word with a latency of 12 clock cycles. The 14-bit word of each channel is serialized and
output as LVDS levels. In addition to the data streams, a bit clock and frame clock are also output. The frame
clock is aligned with the 14-bit word boundary.
ANALOG INPUT
The analog input consists of a switched-capacitor based differential sample and hold architecture, shown in
Figure 82. This differential topology results in very good AC performance even for high input frequencies. The
INP and INM pins have to be externally biased around a common-mode voltage of 1.5 V, available on VCM pin
13. 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 2-V
PP
differential input swing. The maximum swing is determined by the internal
reference voltages REFP (2.0 V nominal) and REFM (1.0 V, nominal). The sampling circuit has a 3 dB bandwidth
that extends up to 500 MHz (see Figure 83, shown by the transfer function from the analog input pins to the
voltage across the sampling capacitors, TF_ADC).
Figure 82. Input Sampling Circuit
48 Submit Documentation Feedback Copyright © 2007–2009, Texas Instruments Incorporated
Product Folder Link(s): ADS6445, ADS6444 ADS6443, ADS6442