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2. Suppose first that we want to measure the temperature of a room with the following components. Direct connection Vcc = 3.3 V LM35 ADC The sensor is the LM35 chip, which gives a voltage proportional to temperature in degrees of Celsius so that 0°C gives zero voltage. The scaling factor is 10 mV/°C, indicating that the LM35 gives 200mV at 20°C and so on. The sensor is a silicon IC, not a thermistor. Its output is a linear function of temperature, which is convenient, but the voltage is small. a) Suppose the ADC is a 10-bit SAR, common in small microcontrollers, which takes its reference from the supply at 3.3V. We wish to resolve changes of 0.1°C or better over a range of 5°C to 30°C. Suppose first that we connect the output of the LM35 directly to the input of the ADC. What voltages must we measure? Is it possible to meet this specification without further components? Why? b) If the specifications in a) cannot be met. You can use an external ADC with a better resolution. Assume that it works over the same range of voltage, 3.3V. Would a 12-bit ADC meet the specifications? Why? c) An alternative solution with a 10-bit ADC is to amplify the output signal of LM35. Please find the gain of the following signal conditioning circuit (amplifier) and determine if the following circuit would meet the same specifications in a). Please show your analysis.

2. Suppose first that we want to measure the temperature of a room with the following components. Direct connection Vcc = 3.3 V LM35 ADC The sensor is the LM35 chip, which gives a voltage proportional to temperature in degrees of Celsius so that 0°C gives zero voltage. The scaling factor is 10 mV/°C, indicating that the LM35 gives 200mV at 20°C and so on. The sensor is a silicon IC, not a thermistor. Its output is a linear function of temperature, which is convenient, but the voltage is small. a) Suppose the ADC is a 10-bit SAR, common in small microcontrollers, which takes its reference from the supply at 3.3V. We wish to resolve changes of 0.1°C or better over a range of 5°C to 30°C. Suppose first that we connect the output of the LM35 directly to the input of the ADC. What voltages must we measure? Is it possible to meet this specification without further components? Why? b) If the specifications in a) cannot be met. You can use an external ADC with a better resolution. Assume that it works over the same range of voltage, 3.3V. Would a 12-bit ADC meet the specifications? Why? c) An alternative solution with a 10-bit ADC is to amplify the output signal of LM35. Please find the gain of the following signal conditioning circuit (amplifier) and determine if the following circuit would meet the same specifications in a). Please show your analysis.

Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
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2. Suppose first that we want to measure the temperature of a room with the following components. Direct connection Vcc = 3.3 V LM35 ADC The sensor is the LM35 chip, which gives a voltage proportional to temperature in degrees of Celsius so that 0°C gives zero voltage. The scaling factor is 10 mV/°C, indicating that the LM35 gives 200mV at 20°C and so on. The sensor is a silicon IC, not a thermistor. Its output is a linear function of temperature, which is convenient, but the voltage is small. a) Suppose the ADC is a 10-bit SAR, common in small microcontrollers, which takes its reference from the supply at 3.3V. We wish to resolve changes of 0.1°C or better over a range of 5°C to 30°C. Suppose first that we connect the output of the LM35 directly to the input of the ADC. What voltages must we measure? Is it possible to meet this specification without further components? Why? b) If the specifications in a) cannot be met. You can use an external ADC with a better resolution. Assume that it works over the same range of voltage, 3.3V. Would a 12-bit ADC meet the specifications? Why? c) An alternative solution with a 10-bit ADC is to amplify the output signal of LM35. Please find the gain of the following signal conditioning circuit (amplifier) and determine if the following circuit would meet the same specifications in a). Please show your analysis. 90k2 ADC LM35 10k2
Transcribed Image Text:2. Suppose first that we want to measure the temperature of a room with the following components. Direct connection Vcc = 3.3 V LM35 ADC The sensor is the LM35 chip, which gives a voltage proportional to temperature in degrees of Celsius so that 0°C gives zero voltage. The scaling factor is 10 mV/°C, indicating that the LM35 gives 200mV at 20°C and so on. The sensor is a silicon IC, not a thermistor. Its output is a linear function of temperature, which is convenient, but the voltage is small. a) Suppose the ADC is a 10-bit SAR, common in small microcontrollers, which takes its reference from the supply at 3.3V. We wish to resolve changes of 0.1°C or better over a range of 5°C to 30°C. Suppose first that we connect the output of the LM35 directly to the input of the ADC. What voltages must we measure? Is it possible to meet this specification without further components? Why? b) If the specifications in a) cannot be met. You can use an external ADC with a better resolution. Assume that it works over the same range of voltage, 3.3V. Would a 12-bit ADC meet the specifications? Why? c) An alternative solution with a 10-bit ADC is to amplify the output signal of LM35. Please find the gain of the following signal conditioning circuit (amplifier) and determine if the following circuit would meet the same specifications in a). Please show your analysis. 90k2 ADC LM35 10k2
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