1.0 Functional Description
The ADC07D1520 is a versatile A/D Converter with an innovative architecture permitting very high speed operation. The controls
available ease the application of the device to circuit solutions. Optimum performance requires adherence to the provisions dis-
cussed here and in the Applications Information Section.
While it is generally poor practice to allow an active pin to float, pins 4, 14, 52 and 127 of the ADC07D1520 are designed to be left
floating without jeopardy. In all discussions for pins 4, 14, and 127, whenever a function is called by allowing these control pins to
float, connecting that pin to a potential of one half the VA supply voltage will have the same effect as allowing it to float.
1.1 OVERVIEW
The ADC07D1520 uses a calibrated folding and interpolating architecture that achieves 6.8 effective bits. The use of folding am-
plifiers greatly reduces the number of comparators and power consumption. Interpolation reduces the number of front-end amplifiers
required, minimizing the load on the input signal and further reducing power requirements. In addition to correcting other non-
idealities, on-chip calibration reduces the INL bow often seen with folding architectures. The result is an extremely fast, high
performance, low power converter.
The analog input signal that is within the converter's input voltage range is digitized to seven bits at speeds of 200 MSPS to 1.5
GSPS. Differential input voltages below negative full-scale will cause the output word to consist of all zeroes. Differential input
voltages above positive full-scale will cause the output word to consist of all ones. Either of these conditions at either the I- or Q-
channel will cause the Out of Range (OR) output to be activated. This single OR output indicates when the output code from one
or both of the channels is below negative full scale or above positive full scale. When PDQ is asserted, the OR indication applies
to the I channel only.
For Non-DES Modes, each converter has a selectable output demultiplexer which feeds two LVDS buses. If the 1:2 Demux Mode
is selected, the output data rate is reduced to half the input sample rate on each bus. When Non-demux Mode is selected, the
output data rate on channels DI and DQ are at the same rate as the input sample clock.
The output levels may be selected to be normal or reduced. Using reduced levels saves power but could result in erroneous data
capture of some or all of the bits, especially at higher sample rates and in marginally designed systems.
1.1.1 Calibration
A calibration is performed upon power-up and can also be invoked by the user upon command. Calibration trims the 100Ω analog
input differential termination resistor and minimizes full-scale error, offset error, DNL and INL, resulting in maximizing SNR, THD,
SINAD (SNDR) and ENOB. Internal bias currents are also set during the calibration process. All of this is true whether the calibration
is performed upon power up or is performed upon command. Running the calibration is required for proper operation and to obtain
the ADC's specified performance. In addition to the requirement to be run at power-up, an on-command calibration must be run
whenever the sense of the FSR pin is changed. For best performance, it is recommend that an on-command calibration be run 20
seconds or more after application of power and whenever the operating temperature changes significantly, relative to the specific
system performance requirements. See 2.4.2.2 On-Command Calibration for more information. Calibration cannot be initiated or
run while the device is in the power-down mode. See 1.1.7 Power Down for information on the interaction between Power Down
and Calibration.
In normal operation, calibration is performed just after application of power and whenever a valid calibration command is given,
which may be accomplished one of two ways, via the CAL pin (30) or the Calibration register (Addr: 0h, Bit 15). The calibration
command is achieved by holding the CAL pin low for at least tCAL_L clock cycles, and then holding it high for at least another
tCAL_H clock cycles, as defined in the Converter Electrical Characteristics. The time taken by the calibration procedure is specified
as tCALin Converter Electrical Characteristics. Holding the CAL pin high upon power up will prevent the calibration process from
running until the CAL pin experiences the above-mentioned tCAL_L clock cycles followed by tCAL_H clock cycles.
CalDly (pin 127) is used to select one of two delay times that take place from the application of power to the start of calibration.
This calibration delay time is dependent on the setting of the CalDly pin and is specified as tCalDly in the Converter Electrical
Characteristics. These delay values allow the power supply to come up and stabilize before calibration takes place. If the PD pin
is high upon power-up, the calibration delay counter will be disabled until the PD pin is brought low. Therefore, holding the PD pin
high during power up will further delay the start of the power-up calibration cycle. The best setting of the CalDly pin depends upon
the power-on settling time of the power supply.
1.1.2 Acquiring the Input
In 1:2 Demux Non-DES Mode, data is acquired at the falling edge of CLK+ (pin 18) and the digital equivalent of that data is available
at the digital outputs 13 input clock cycles later for the DI and DQ output buses and 14 input clock cycles later for the DId and DQd
output buses. See Pipeline Delay in the Converter Electrical Characteristics. There is an additional internal delay called tOD before
the data is available at the outputs. See the Timing Diagrams. The ADC07D1520 will convert as long as the input clock signal is
present. The fully differential comparator design and the innovative design of the sample-and-hold amplifier, together with self
calibration, enables a very flat SINAD/ENOB response beyond 1.5 GHz. The ADC07D1520 output data signaling is LVDS and the
output format is offset binary.
1.1.3 Control Modes
Much of the user control can be accomplished with several control pins that are provided. Examples include initiation of the cali-
bration cycle, power down mode and full scale range setting. However, the ADC07D1520 also provides an Extended Control Mode
whereby a serial interface is used to access register-based control of several advanced features. The Extended Control Mode is
not intended to be enabled and disabled dynamically. Rather, the user is expected to employ either the Non-extended Control
Mode or the Extended Control Mode at all times. When the device is in the Extended Control Mode, pin-based control of several
ADC07D1520
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