Datasheet

22
LTC1096/LTC1096L
LTC1098/LTC1098L
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Effective Number of Bits
The effective number of bits (ENOBs) is a measurement of
the resolution of an A/D and is directly related to the
S/(N + D) by the equation:
ENOB = [S/(N + D) –1.76]/6.02
where S/(N + D) is expressed in dB. At the maximum
sampling rate of 33kHz the LTC1096 maintains 7.5 ENOBs
or better to 40kHz. Above 40kHz the ENOBs gradually
decline, as shown in Figure 12, due to increasing second
harmonic distortion. The noise floor remains approxi-
mately 70dB.
Figure 12. Dynamic Accuracy Is Maintained Up to an Input
Frequency of 40kHz
INPUT FREQUENCY (kHz)
0
EFFECTIVE NUMBER OF BITS (ENOBs)
3
4
5
LTC1096/8 • F12
2
1
0
20 40
6
7
8
f
SAMPLE
= 31.25kHz
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MICROPROCESSOR INTERFACES
The LTC1096(L)/LTC1098(L) can interface directly (with-
out external hardware to most popular microprocessor
(MPU) synchronous serial formats (see Table 1). If an
MPU without a dedicated serial port is used, then three or
four of the MPU’s parallel port lines can be programmed
to form the serial link to the LTC1096(L)/LTC1098(L).
Included here is one serial interface example and one
example showing a parallel port programmed to form the
serial interface.
Motorola SPI (MC68HC05C4,CM68HC11)
The MC68HC05C4 has been chosen as an example of
an MPU with a dedicated serial port. This MPU transfer
data MSB-first and in 8-bit increments. With two 8-bit
transfers, the A/D result is read into the MPU. The first
8-bit transfer sends the D
IN
word to the LTC1098(L)
and clocks into the processor. The second 8-bit trans-
fer clocks the A/D conversion result, B7 through B0,
into the MPU.
ANDing the first MUP received byte with 00Hex clears the
first byte. Notice how the position of the start bit in the first
MPU transmit word is used to position the A/D result
right-justified in two memory locations.
Table 1. Microprocessor with Hardware Serial Interfaces
Compatible with the LTC1096(L)/LTC1098(L)
* Requires external hardware
MICROWIRE and MICROWIRE/PLUS are trademarks of
National Semiconductor Corp.
PART NUMBER TYPE OF INTERFACE
Motorola
MC6805S2,S3 SPI
MC68HC11 SPI
MC68HC05 SPI
RCA
CDP68HC05 SPI
Hitachi
HD6305 SCI Synchronous
HD63705 SCI Synchronous
HD6301 SCI Synchronous
HD63701 SCI Synchronous
HD6303 SCI Synchronous
HD64180 CSI/O
National Semiconductor
COP400 Family MICROWIRE
TM
COP800 Family MICROWIRE/PLUS
TM
NS8050U MICROWIRE/PLUS
HPC16000 Family MICROWIR/PLUS
Texas Instruments
TMS7002 Serial Port
TMS7042 Serial Port
TMS70C02 Serial Port
TMS70C42 Serial Port
TMS32011* Serial Port
TMS32020 Serial Port