Philips Semiconductors

Preliminary specification

83C749/87C749

80C51 8-bit microcontroller family

2K/64 OTP/ROM, 5 channel 8-bit A/D, PWM, low pin count

1998 Apr 23

10

INPUT

To Comparator

+

Multiplexer

Rm = 0.5 - 3 k

Ω

CS + CC = 15pF maximum

RS = Recommended < 9.6 k

Ω for 1 LSB @ 12MHz

NOTE:

Because the analog to digital converter has a sampled-data comparator, the input looks capacitive to a source. When a conversion

is initiated, switch Sm closes for 8tcy (8

µs @ 12MHz crystal frequency) during which time capacitance Cs + Cc is charged. It should

be noted that the sampling causes the analog input to present a varying load to an analog source.

SU00199

Figure 2. A/D Input: Equivalent Circuit

A/D CONVERTER PARAMETER DEFINITIONS

The following definitions are included to clarify some specifications

given and do not represent a complete set of A/D parameter

definitions.

Absolute Accuracy Error

Absolute accuracy error of a given output is the difference between

the theoretical analog input voltage to produce a given output and

the actual analog input voltage required to produce the same code.

Since the same output code is produced by a band of input voltages,

the “required input voltage” is defined as the midpoint of the band of

input voltage that will produce that code. Absolute accuracy error

not specified with a code is the maximum over all codes.

Nonlinearity

If a straight line is drawn between the end points of the actual

converter characteristics such that zero offset and full scale errors

are removed, then non-linearity is the maximum deviation of the

code transitions of the actual characteristics from that of the straight

line so constructed. This is also referred to as relative accuracy and

also integral non-linearity.

Differential Non-Linearity

Differential non-linearity is the maximum difference between the

actual and ideal code widths of the converter. The code widths are

the differences expressed in LSB between the code transition

points, as the input voltage is varied through the range for the

complete set of codes.

Gain Error

Gain error is the deviation between the ideal and actual analog input

voltage required to cause the final code transition to a full-scale

output code after the offset error has been removed. This may

sometimes be referred to as full scale error.

Offset Error

Offset error is the difference between the actual input voltage that

causes the first code transition and the ideal value to cause the first

Channel to Channel Matching

Channel to channel matching is the maximum difference between

the corresponding code transitions of the actual characteristics

taken from different channels under the same temperature, voltage

and frequency conditions.

Crosstalk

Crosstalk is the measured level of a signal at the output of the

converter resulting from a signal applied to one deselected channel.

Total Error

Maximum deviation of any step point from a line connecting the ideal

first transition point to the ideal last transition point.

Relative Accuracy

Relative accuracy error is the deviation of the ADC’s actual code

transition points from the ideal code transition points on a straight

line which connects the ideal first code transition point and the final

code transition point, after nullifying offset error and gain error. It is

generally expressed in LSBs or in percent of FSR.