1°C Triple Temperature Sensor with Resistance Error Correction
Datasheet
VDD
Ilow
Ibias
Ihigh
Delta Vbe
Sample
&
11-bit Output
1-bit
Digital
Averaging
Filter
delta-sigma
Modulator
Hold
Internal or
Bias
Diode
Remote Diode
Figure 4.2 Detailed Block Diagram
Figure 4.2 shows a detailed block diagram of the temperature measurement circuit. The EMC1023
incorporates switched capacitor technology that integrates the temperature diode ∆VBE from different
bias currents. The negative terminal, DN, for the temperature diode is internally biased with a forward
diode voltage referenced to ground.
The advantages of this architecture over Nyquist rate FLASH or SAR converters are superb linearity
and inherent noise immunity. The linearity can be directly attributed to the delta-sigma ADC single-bit
comparator while the noise immunity is achieved by the ~20ms integration time which translates to
50Hz input noise bandwidth.
The 11 bit conversion can be displayed in either legacy format or in extended range format. In Legacy
format, the temperature range covers –64ºC to 127ºC while in extended format, temperature readings
span -64ºC to 191ºC. It should be noted that the latter range is really meant to cover thermal diodes
with a non ideal curvature caused by factor n in equation (1) not being equal to exactly 1.000. In
general, it is not recommended to run silicon based thermal diodes at temperatures above 150ºC.
4.2
4.3
Resistance Error Correction
The EMC1023 includes resistance error correction implemented in the analog front end of the chip.
Without this automatic feature, voltage developed across the parasitic resistance in the remote diode
path causes the temperature to read higher than the true zone temperature. The error introduced by
parasitic resistance is approximately +0.7ºC per ohm. Sources of parasitic resistance include bulk
resistance in the remote temperature transistor junctions along with resistance in the printed circuit
board traces and package leads.
Resistance error correction in the EMC1023 eliminates the need to characterize and compensate for
parasitic resistance in the remote diode path.
Programmable Ideality Factor Configuration
Temperature sensors like the EMC1023 are typically designed for remote diodes with an ideality factor
of 1.008. When the diode does not have this exact factor, an error is introduced in the temperature
measurement. Programmable offset registers are sometimes used to compensate for this error, but
this correction is only perfect at one temperature since the error introduced by ideality factor mismatch
is a function of temperature. The higher the temperature measured, the greater the error introduced.
To provide maximum flexibility to the user, the EMC1023 provides a 6-bit ideality factor register for
each remote diode. The ideality factor of the remote diode is programmed in these registers to
eliminate errors across all temperatures. See Section 4.10, "Ideality Factor Register," on page 15 for
details on programming these registers.
Revision 1.2 (04-15-05)
SMSC EMC1023
DATA1S0HEET
SMSC [ SMSC CORPORATION ]
