THS12082

12-BIT, 8 MSPS, SIMULTANEOUS SAMPLING ANALOG-TO-DIGITAL CONVERTERS

SLAS271 – MAY 2000

9

POST OFFICE BOX 655303

detailed description

reference voltage

The THS12082 has a built-in reference, which provides the reference voltages for the ADC. VREFP is set to

3.5 V and VREFM is set to 1.5 V. An external reference can also be used through two reference input pins, REFP

and REFM, if the reference source is programmed as external. The voltage levels applied to these pins establish

the upper and lower limits of the analog inputs to produce a full-scale and zero-scale reading respectively.

analog inputs

The THS12082 consists of two analog inputs, which are sampled simultaneously. These inputs can be selected

individually and configured as single-ended or differential inputs. The desired analog input channel can be

programmed.

analog-to-digital converter

The THS12082 uses a 12-bit pipelined multistaged architecture with four 1-bit stages followed by four 2-bit

stages, which achieves a high sample rate with low power consumption. The THS12082 distributes the

conversion over several smaller ADC subblocks, refining the conversion with progressively higher accuracy as

the device passes the results from stage to stage. This distributed conversion requires a small fraction of the

number of comparators used in a traditional flash ADC. A sample-and-hold amplifier (SHA) within each of the

stages permits the first stage to operate on a new input sample while the second through the eighth stages

operate on the seven preceding samples.

conversion modes

The conversion can be performed in two different conversion modes. In the single conversion mode, the

conversion is initiated by an external signal (CONVST). An internal oscillator controls the conversion time. In

the continuous conversion mode, an external clock signal is applied to the clock input (CONV_CLK). A new

conversion is started with every falling edge of the applied clock signal.

sampling rate

The maximum possible conversion rate per channel is dependent on the selected analog input channels. Table

1 shows the maximum conversion rate in the continuous conversion mode for different combinations.

Table 1. Maximum Conversion Rate

CHANNEL CONFIGURATION

NUMBER OF CHANNELS

MAXIMUM CONVERSION

RATE PER CHANNEL

1 single-ended channel

1

8 MSPS

2 single-ended channels

2

4 MSPS

1 differential channel

1

8 MSPS

The maximum conversion rate in the continuous conversion mode per channel, fc, is given by:

fc

+ 8 MSPS

# channels

Table 2 shows the maximum conversion rate in the single conversion mode.