HMCAD1100 Datasheet, PDF (23/26 Pages) Hittite Microwave Corporation – Octal 13/12-Bit 20/40/50 MSPS A/D Co nverter

v03.0611
HMCAD1100
Octal 13/12-Bit 20/40/50 MSPS
A/D Converter
0
0 - 23
Table 11: Performance Control Settings
perfm_cntrl <2:0>
Analog power dissipation
111
000 (default)
001
010
011
-10%
Nominal
Do not use
Do not use
Do not use
The ext_vcm_bc register controls the driving strength in the buffer supplying the voltage on the VCM pin. If this pin is
not in use, the buffer can be switched off. If current is drawn from the VCM pin, the driving strength can be increased
to keep the voltage on this pin at the correct level.
Table 12: External Common
Mode Voltage Buffer Driving Strength
ext_vcm_bc
<1:0>
00
01 (default)
10
11
VCM buffer driving strength [µA] Max current
sinked/sourced from VCM pin with < 50 mV
voltage change.
Off (VCM floating)
±6.5
±70
±140
Theory of Operation
HMCAD1100 is an 8-channel, high-speed, CMOS
ADC. The 13 bits given out by each channel are
serialized to 12 or 14 bits and sent out on a single
pair of pins in LVDS format. All eight channels of
HMCAD1100 operate from one clock input, which can
be differential or single ended. The sampling clocks
for each of the eight channels are generated from
the clock input using a carefully matched clock buffer
tree. The 12x/14x clock required for the serializer is
generated internally from FCLK using a phase-locked
loop (PLL). A 6x/7x and 1x clock are also output in
LVDS format, along with the data to enable easy
data capture. HMCAD1100 uses internally generated
references. The differential reference value is 1V. This
results in a differential input of −1V to correspond to
the zero code of the ADC, and a differential input of
+1V to correspond to the full-scale code (code 8191).
The ADC employs a pipelined converter architecture.
Each stage feeds its output data into the digital error
correction logic, ensuring excellent differential linearity
and no missing codes at 13-bit level.
HMCAD1100 operates from two sets of supplies
and grounds. The analog supply and ground set is
identified as AVDD and AVSS, while the digital set is
identified by DVDD and DVSS.
Recommended Usage
Analog Input
The analog input to HMCAD1100 is a switched
capacitor track-and-hold amplifier optimized for
differential operation. Operation at common mode
voltages at mid supply is recommended even if
performance will be good for the ranges specified.
The VCM pin provides a voltage suitable as common
mode voltage reference. The internal buffer for
the VCM voltage can be switched off, and driving
capabilities can be changed programming the ext_
vcm_bc<1:0> register.
Figure 11. Input configuration
Figure 12 shows a simplified drawing of the input
network. The signal source must have sufficiently low
output impedance to charge the sampling capacitors
For price, delivery and to place orders: Hittite Microwave Corporation, 2 Elizabeth Drive, Chelmsford, MA 01824
978-250-3343 tel • 978-250-3373 fax • Order On-line at www.hittite.com
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