National Semiconductor ADC10040, User Manual

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http://www.national.com
1.0 Introduction
The ADC10080EVAL Design Kit (consisting of the Evaluation Board
and this manual) is designed to ease evaluation and design-in of
National's ADC10040, ADC10065, or ADC10080 10-bit Analog-to-
Digital Converters, which operate at speeds up to 40, 65, and 80
MSPS. Further reference in this manual to the ADC10080 is meant
to also include the ADC10040 and the ADC10065 unless otherwise
specified. The latest datasheet for these products can be obtained
from http://www.national.com.
The evaluation board can be used in either of two modes. In the
Manual mode, suitable test equipment, such as a logic analyzer,
can be used with the board to evaluate the ADC10080 performance.
In the Computer mode, evaluation is simplified by connecting the
board to the WaveVision™ Digital Interface Board (order number
WAVEVSN BRD 4.0). It is connected to a personal computer
through a USB port and running WaveVision™ software, operating
under Microsoft Windows 95 or later. The WaveVision™ software
can perform an FFT on the captured data upon command and, with
the frequency domain plot, shows dynamic performance in the form
of SNR, SINAD, THD and SFDR.
The signal at J1, the Analog Input to the board, is digitized and is
available at pins B4 through B13 of J2 and pins 10 through 19 of
JP4. See the board schematic for more details.
2.0 Quick Start
Refer to the board layout for locations of test points and major
components.
For Stand-Alone operation:
1. Select the input voltage range by inserting a jumper into JP1.
Set the jumper on pins 1&2 for 2.0 Vpp. Set the jumper on pins
2&3 for 1.5 Vpp. If no jumper is inserted, 1.0 Vpp is assumed.
2. To make the ADC10080 active, insure there is no jumper on
JP3.
3. Select the output data format using JP2. When the jumper is
on pins 1&2, 2’s complement data format is selected. If the
jumper is on pins 2&3, offset binary is selected.
4. Connect a clean power supply to Power Connector JS1. Refer
to Table 1 for power supply description and requirements.
5. Connect a signal of the selected amplitude (see step 1) from a
50-Ohm source to Analog Input BNC J1. Insure that the signal
is not over-ranged, by examining a histogram. (Either by using
WaveVision
tm
, or the logic analyzer being used.) Over-range
signals will dramatically increase the THD.
6. The digitized signal is available at pins B4 through B13 of J2
and pins 10 through 19 of JP4.
JS1 pin
number
Description Voltage
Range
1 Vcc for Crystal and
VDDA for
ADC10080
2.7 - 3.3 V
2 Ground 0V
3 VDDIO 2.5 – 3.3 V
4 Output Buffer VCC 4.9 – 5.1 V
Table 1
For Computer mode operation:
1. Connect the evaluation board to the WaveVision
tm
Digital
Interface Board. See the instruction manual supplied with the
WaveVision
tm
kit. The latest WaveVision
tm
software can be
obtained from http://www.national.com.
2. Select the input voltage range by inserting a jumper into JP1.
Set the jumper on pins 1&2 for 2.0 Vpp. Set the jumper on pins
2&3 for 1.5 Vpp. If no jumper is inserted, 1.0 Vpp is assumed.
3. To make the ADC10080 active, insure there is no jumper on
JP3.
4. Select pins 2&3 on JP2 so that the output data is offset binary.
5. Connect a clean power supply to Power Connector JS1. Refer
to Table 1 for power supply description and requirements.
6. If the output level goes over range as seen on the data
captured through WaveVision™, reduce the output level from
the signal generator and capture data again. If the output level
does not reach codes of 25 and 1000, increase the output level
from the signal generator and capture data again.
3.0 Functional Description
The ADC10080 Evaluation Board schematic is shown in Section 5 .
3.1 The Signal Input
The signal transformer T1 provides single-ended to differential
conversion. The common mode voltage VCOM provided by the
chip, sets the common mode of the input signal by biasing the
center tap of T1.
The differential signal present on the secondary side of the
transformer is then sent through a low pass filter set up by R1, R5 &
C9.
It is important when evaluating the dynamic performance of the
ADC10080 (or any A/D converter), that a clean sine wave be
presented to the converter. To do this it is necessary to use a
bandpass or a low pass filter between the signal source and the
ADC10080 evaluation board input J1. Even the best signal
generators available do not provide adequate noise and distortion
performance for proper evaluation of a 10-bit ADC. A high-quality
bandpass filter with better than 12-bit equivalent noise
characteristics and at least 80dB stop band attenuation is ideal. No
scope or other test equipment should be connected to any input
circuitry while gathering data.
3.2 Digital Data Output.
The digital output data from the ADC10080 is available at the 96-pin
Euro connector J2 and header JP4. Series resistors R7 – R17
provide data line dampening that may occur with long cables. U3
provides buffering to drive the cable. U3’s VCC may be adjusted for
various output levels. Refer to Table 1 for voltage range.
3.3 ADC10080 Control Pins.
The ADC10080 has three control pins, making it a very versatile
converter. They are Standby (Pin 28 – STBY), Data Format (Pin 15
– DF) and Input Range Select (Pin 5 – IRS).
3.3.1 The Standby (STBY) Pin
When this pin is pulled high (pins 1&2 of JP3 are connected), the
converter is put into ‘standby’ mode. The converter consumes only
13.5 mW of power. When STBY is tied to VSSA (JP3 is open), the
ADC is in full operation.
3.3.2 The Data Format (DF) pin
This pin sets the output data format of the ADC10080. When this
pin is pulled to VDDA (pins 1&2 of JP2 are connected), the output is
2’s complement. When pulled down to VSSA (pins 2&3 of JP2 are
connected), the data output is offset binary.