THS1030_13 Datasheet, PDF(14/39 Page) Texas Instruments – 3-V TO 5.5-V, 10-BIT, 30MSPS CMOS ANALOG-TO-DIGITAL CONVERTER

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THS1030_13 Datasheet, PDF (14/39 Pages) Texas Instruments – 3-V TO 5.5-V, 10-BIT, 30MSPS CMOS ANALOG-TO-DIGITAL CONVERTER

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THS1030

3ÄV TO 5.5ÄV, 10ÄBIT, 30 MSPS

CMOS ANALOGÄTOÄDIGITAL CONVERTER

SLAS243E â NOVEMBER 1999 â REVISED DECEMBER 2003

PRINCIPLES OF OPERATION

ADC reference generation

The THS1030 has three primary modes of ADC reference generation, selected by the voltage level applied to

the MODE pin.

Connecting the MODE pin to AGND gives full external reference mode. In this mode, the user supplies the ADC

reference voltages directly to pins REFTF and REFBF. This mode is used where there is need for minimum

power drain or where there are very tight tolerances on the ADC reference voltages. This mode also offers the

possibility of Kelvin connection of the reference inputs to the THS1030 to eliminate any voltage drops from

remote references that may occur in the system. Only single-ended input is possible in this mode.

Connecting the MODE pin to AVDD/2 gives differential mode. In this mode, the ADC reference voltages REFTF

and REFBF are generated by the internal reference buffer from the voltage applied to the VREF pin. This mode

is suitable for handling differentially presented inputs, which are applied to the AIN and REFTS/REFBS pins.

A special case of differential mode is center span mode, in which the user applies a single-ended signal to AIN

and applies the mid-scale input voltage (VM) to the REFTS and REFBS pins.

Connecting the MODE pin to AVDD gives top/bottom mode. In this mode, the ADC reference voltages REFTF

and REFBF are generated by the internal reference buffer from the voltages applied to the REFTS and REFBS

pins. Only single-ended input is possible in top/bottom mode.

When MODE is connected to AGND, the internal reference buffer is powered down, its inputs and outputs

disconnected, and REFTS and REFBS internally connected to REFTF and REFBF respectively. These nodes

are connected by the user to external sources to provide the ADC reference voltages. The internal connections

are designed for use in kelvin connection mode (Figure 14). When using external reference mode as shown

in Figure 13, REFTS must be shorted to REFTF and REFBS must be shorted to REFBF externally. The mean

of REFTF and REFBF must be equal to AVDD/2. See Figure 13.

Table 1. Typical Set of Reference Connections

REFERENCE MODE

External

Internal

External (through internal

reference buffer)

Output of VREF can be

externally tied to REFTS or

REFBS to provide one of the

reference voltages

MODE REFSENSE

VREF

VOLTAGE

AGND AVDD

AVDD/2

VREF

AGND

External

divider

AVDD

VREF

AGND

External

divider

Disabled

1 + Ra/Rb

(see Figure 22)

Disabled

1 + Ra/Rb

(see Figure 22)

REFTS, REFBS

Reference buffer powered

down, reference voltage

provided directly by REFT

and REFB

Externally connect REFTS to

REFBS. This pair then forms

AINâ to the ADC.

REFTS = VFS+

REFBS = VFSâ

ANALOG INPUT FIGURES

Single-ended

12, 13, 14

Differential or

center span

15, 16, 17

Single-ended

(top-bottom

mode)

18, 19

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