**PERFORMANCE OF THE LTC1650**

**16-BIT DIGITAL-TO-ANALOG CONVERTER AT CRYOGENIC TEMPERATURES**

Test Report

Scott Gerber

ZIN Technologies

&

Ahmad Hammoud

QSS Group, Inc.

NASA Glenn Research Center

Cleveland, Ohio

June 12, 2001

**Performance of the LTC1650**

**16-Bit Digital-To-Analog Converter at Cryogenic Temperatures**

**Background**

The Linear Technology LTC1650 is a 16-bit digital-to-analog converter
(DAC) that is capable of unipolar or bipolar output swing. It features a
digital three-wire cascadable serial input interface and has excellent
accuracy over its full operating temperature range with very low power
dissipation. The device rail-to-rail buffered output can source or sink
a current of 5 mA over the entire specified operating range \[1\].

**Test Setup**

Three industrial-grade (AIN) devices of the LTC1650 DAC were evaluated
from room temperature to ‑190 °C in a liquid nitrogen cooled chamber.
Test were performed at temperatures of 25, -25, -50, -100, ‑150, ‑170,
-180 and ‑190 °C. At each test temperature, the device was allowed to
soak for 10 minutes before measurements were made.

The devices were evaluated in terms of their analog converted output
characteristics and the internal reference resistance. The device output
was configured for unipolar operation with no external load connected.
The applied voltages to the reference inputs (REFHI) and (REFLO) pins
were 4.0V and 0V, respectively. This allowed an output voltage swing of
0V to 4.0V. The serial digital input, which included the input to the
clock (CLK), the chip select/data load ($\overline{\text{CS}}$/LD), and
the 16-bit data word (DIN), was supplied via a pattern generator that
was programmed to produce a specific output voltage.

Thermal cycling was also performed on the three devices in the
temperature range of +85 °C to -190 °C for a total of ten cycles. A
temperature rate of change of 15 °C /min was used. During each cycle,
the device under test was allowed to soak for 20 minutes at the extreme
temperatures, i.e. +85 °C and ‑190 °C.

**Results and Discussion**

The converted analog output of device 1 for various digital input levels
is shown at different test temperatures in Table I. It can be clearly
seen that the analog output level tracks its digital input counterpart
quite well throughout the test temperature range of +25 °C to -190 °C.
The waveform of this output recorded at the extreme temperatures of
25 °C and -190 °C is depicted in Figure 1a and 1b, respectively. The
only apparent changes resulting from the low temperature exposure are
the appearance of a few spikes at the transition times and a slight
increase in the output settling time. These insignificant changes seem
to occur only at temperatures below -170 °C.

The full-scale analog output voltage, which corresponds to a full-scale
digital input of 3.97V, is shown as a function of temperature in Figure
2. The values of this output ranged between 3.978V and 3.992V within the
span of the test temperatures. This translates into a gain error,
excluding the required adjustment of the offset error, of 8 to 22 mV.
Although this gain error far exceeds the manufacturer's specified limit,
it is believed that instrumentation inaccuracies and parasitic
associated with circuit layout, such as long lead wire, might have
contributed to this outcome. These factors might have also contributed
to the appearance of the few spikes and the increase in settling time,
as discussed previously. Nonetheless, the device seemed to produce a
consistent output regardless of the test temperature.

The other parameter of the device that was investigated in this work was
the internal reference resistance. This property seemed to exhibit a
gradual, but very slight, decrease with decrease in temperature as shown
in Figure 3. For example, this decrease amounted to only about 3.7% at
the lowest temperature of ‑190 °C.

Similar to device 1, the other two devices displayed comparable behavior
in their investigated properties with temperature. The results
pertaining to device 2 in terms of its converted analog output, output
waveform, and internal reference resistance are shown in Table II and
Figures 4-6. Likewise, those for device 3 are shown in Table III and
Figures 7-9.

The three devices were also thermal cycled in the temperature range of
+85 °C to -190 °C for a total of ten cycles. During each cycle, the
device under test was allowed to soak for 20 minutes at the extreme
temperatures, i.e. +85 °C and ‑190 °C. The pre-thermal cycling output
waveform for device 1 is shown in Figure 10a and 10b at +85 °C and
‑190 °C, respectively. Those obtained after the fifth and the tenth
final cycle are shown in Figures 11 and 12, respectively. It can be
clearly seen that thermal cycling did not have any significant effect on
the performance of the device as the output voltage waveform was almost
an exact replica under the three conditions, as depicted in Figures
10-12.

Similar to device 1, the other two devices did not undergo any changes
in their output characteristics with thermal cycling. Although the data
pertaining to device 2 and 3 is not presented graphically, their output
waveforms resembled that of device 1.

**Conclusion**

Three devices of the industrial-grade LTC1650AIN 16-bit
digital-to-analog converter were evaluated in terms of their output
characteristics in the temperature range of 25 °C to ‑190 °C. These
devices, which are rated for -40 °C to 85 °C operation, were also
investigated under thermal cycling between +85 °C and ‑190 °C. The
results obtained in this limited investigation indicate that all devices
exhibited good operational behavior in their output characteristics with
temperature. Only minor changes, which included a reduction in the
output settling time and the appearance of a few spikes at the
transition times, seemed to occur at very low temperatures. Further
testing under long term temperature exposure is, however, needed to
establish operational performance and reliability of these devices and
to determine their suitability for low temperature applications.

**References**

1\. LTC1650 Low Glitch 16-Bit Voltage Output DAC Data Sheet, Linear
Technology.

**Acknowledgments**

This work was performed under the NASA Glenn Research Center GESS
Contract \# NAS3-00145.

Table I. Analog converted outputs for device 1 as a function of
temperature.

  --------- ----------- -------- ----------- ----------- ----------- ----------- ----------- -----------
            **Digital                                                                        
            Input                                                                            
            Voltage                                                                          
            (V)**                                                                            

            **3.97**    **0**    **0.662**   **1.323**   **2.432**   **2.779**   **3.474**   **1.615**

  **Temp    **Analog                                                                         
  (°C)**    Output                                                                           
            Voltage                                                                          
            (V)**                                                                            

  25        3.978       -0.053   0.622       1.298       2.427       2.782       3.485       1.593

  -25       3.983       -0.044   0.637       1.31        2.437       2.792       3.495       1.61

  -50       3.991       -0.039   0.639       1.313       2.439       2.791       3.493       1.604

  -100      3.992       -0.04    0.638       1.316       2.442       2.79        3.494       1.606

  -150      3.986       -0.046   0.626       1.303       2.431       2.781       3.486       1.592

  -170      3.983       -0.048   0.624       1.298       2.426       2.779       3.478       1.597

  -180      3.983       -0.047   0.627       1.3         2.429       2.78        3.48        1.591

  -190      3.985       -0.06    0.624       1.3         2.425       2.78        3.48        1.59

  25        3.983       -0.053   0.623       1.302       2.433       2.782       3.484       1.591
  --------- ----------- -------- ----------- ----------- ----------- ----------- ----------- -----------

![](media/image1.emf){width="6.413888888888889in"
height="2.0708333333333333in"}

Figure 1. Output voltage waveforms for device 1 at 25°C and -190°C.

![](media/image2.emf){width="6.475in" height="2.401388888888889in"}

Figure 2. Device 1 full-scale voltage versus temperature. Figure 3.
Device 1 reference resistance versus temperature.

Table II. Analog converted outputs for device 2 as a function of
temperature.

  --------- ----------- -------- ----------- ----------- ---------- --------- --------- -----------
            **Digital                                                                   
            Input                                                                       
            Voltage                                                                     
            (V)**                                                                       

            **4**       **0**    **0.667**   **1.333**   **2.45**   **2.8**   **3.5**   **1.627**

  **Temp    **Analog                                                                    
  (°C)**    Output                                                                      
            Voltage                                                                     
            (V)**                                                                       

  25        4.02        -0.032   0.651       1.33        2.461      2.81      3.518     1.619

  -25       4.01        -0.03    0.653       1.33        2.461      2.814     3.516     1.619

  -50       4.014       -0.027   0.654       1.331       2.459      2.81      3.51      1.618

  -100      4.013       -0.028   0.651       1.33        2.457      2.81      3.513     1.618

  -150      4.008       -0.03    0.654       1.329       2.457      2.81      3.512     1.618

  -170      4.019       -0.029   0.654       1.33        2.463      2.814     3.518     1.619

  -180      4.01        -0.031   0.652       1.331       2.46       2.811     3.513     1.619

  -190      4.013       -0.032   0.65        1.33        2.461      2.813     3.516     1.619

  25        4.011       -0.031   0.649       1.328       2.46       2.813     3.515     1.618
  --------- ----------- -------- ----------- ----------- ---------- --------- --------- -----------

![](media/image3.emf){width="6.413888888888889in"
height="2.0708333333333333in"}

Figure 4. Output voltage waveforms for device 2 at 25°C and -190°C.

![](media/image4.emf){width="6.475in" height="2.401388888888889in"}

Figure 5. Device 2 full-scale voltage versus temperature. Figure 6.
Device 2 reference resistance versus temperature.

Table III. Analog converted outputs for device 3 as a function of
temperature.

  --------- ----------- -------- ----------- ----------- ---------- --------- --------- -----------
            **Digital                                                                   
            Input                                                                       
            Voltage                                                                     
            (V)**                                                                       

            **4**       **0**    **0.667**   **1.333**   **2.45**   **2.8**   **3.5**   **1.627**

  **Temp    **Analog                                                                    
  (°C)**    Output                                                                      
            Voltage                                                                     
            (V)**                                                                       

  25        4.012       -0.03    0.651       1.33        2.457      2.808     3.513     1.617

  -25       4.01        -0.033   0.65        1.325       2.454      2.806     3.51      1.614

  -50       4.016       -0.037   0.646       1.325       2.457      2.811     3.515     1.615

  -100      4.014       -0.036   0.648       1.326       2.456      2.81      3.517     1.615

  -150      4.011       -0.03    0.65        1.33        2.456      2.807     3.51      1.615

  -170      4.014       -0.037   0.646       1.324       2.455      2.806     3.512     1.612

  -180      4.015       -0.036   0.65        1.328       2.458      2.81      3.515     1.616

  -190      4.007       -0.035   0.646       1.323       2.455      2.809     3.51      1.613

  25        4.013       -0.04    0.645       1.327       2.457      2.811     3.515     1.617
  --------- ----------- -------- ----------- ----------- ---------- --------- --------- -----------

![](media/image5.emf){width="6.413888888888889in"
height="2.0708333333333333in"}

Figure 7. Output voltage waveforms for device 3 at 25°C and -190°C.

![](media/image6.emf){width="6.475in" height="2.401388888888889in"}

Figure 8. Device 3 full-scale voltage versus temperature. Figure 9.
Device 3 reference resistance versus temperature.

![](media/image7.emf){width="6.413888888888889in"
height="2.0722222222222224in"}

Figure 10. Pre-thermal cycling output voltage waveforms for device 1.

![](media/image8.emf){width="6.413888888888889in"
height="2.0722222222222224in"}

Figure 11. Output voltage waveforms for device 1after five thermal
cycles.

![](media/image9.emf){width="6.413888888888889in"
height="2.0722222222222224in"}

Figure 12. Output voltage waveforms for device 1 after ten thermal
cycles.