Quiz Driving a SAR ADC with a Fully

Quiz: Driving a SAR ADC with a Fully Differential Amplifier TIPL 4103 TI Precision Labs – ADCs Created by Art Kay 1

Quiz: Linear Range ADC + FDA 1. Design a FDA circuit topology to translate a single ended 0 V to 1 V, to 0 V to 4 V. Use THS 4551, OPA 320, and ADS 9110 with a 4. 096 V reference. Will the output be linear over the full 0 V to 1 V signal range? 2. Design a FDA circuit topology to translate a single ended -0. 1 V to +0. 1 V, to 0 V to 2. 5 V. Use THS 4551, OPA 320, and ADS 9110 with a 2. 5 V reference. Will the output be linear over the full 0 V to 1 V signal range? 3. (T/F) Assume the input signal applied to an FDA has both even and odd order harmonics. The the FDA will cancel the even order harmonics. 4. (T/F) The Vocm pin can be directly connected to a voltage divider to set it’s output common mode. 2

Solutions 3

Quiz: Linear Range ADC + FDA 1. Design a FDA circuit topology to translate a single ended 0 V to 1 V, to 0 V to 4 V. Use THS 4551, OPA 320, and ADS 9110 with a 4. 096 V reference. Will the output be linear over the full 0 V to 1 V signal range? Analog engineer’s calculator used to select U 2 Feedback resistors 4

Quiz: Linear Range ADC + FDA Problem 1: continued. PARAMETER OPA 320 INPUT VOLTAGE Common-mode voltage range OUTPUT Voltage swing from both rails TEST CONDITION Vcm VO MIN TYP MAX (V+)+0. 1 (V-) - 0. 1 RL = 10 kΩ 10 20 RL = 2 kΩ 25 35 UNIT V m. V OPEN-LOOP GAIN Open-loop gain Amplifier input range Amplifier output range Amplifier Linear Range Worst Case Range AOL 0. 1 < Vo < (V+)-0. 1 V, RL = 10 kΩ 0. 2 < Vo < (V+)-0. 2 V, RL = 2 kΩ 114 108 132 123 d. B -0. 1 V < Vcm < 5. 1 V 0. 02 < VO < 4. 98 V 0. 1 < VO < 4. 9 V 5

Quiz: Linear Range ADC + FDA Problem 1: continued. PARAMETER THS 4551 MIN Output voltage low Output voltage high (V+) – 0. 23 (V+) – 1. 2 MAX (V-) + 0. 23 (V+) – 0. 2 (V-) + 0. 2 Common mode input voltage low Common mode input voltage high TYP (V-) + 0. 2 (V+) – 1. 1 UNIT V V (V-) – 0. 1 input range output range V -0. 1 V < Vcm < 3. 8 V 0. 23 < VO < 4. 77 V V Note: The output swing low on the THS limits the range. 6

Quiz: Linear Range ADC + FDA Problem 1: continued. Note: One approach to avoiding the output swing limitation is a -0. 3 V negative supply. 7

Quiz: Linear Range ADC + FDA 2. Design a FDA circuit topology to translate a single ended -0. 1 V to +0. 1 V, to 0 V to 2. 5 V. Use THS 4551, OPA 320, and ADS 9110 with a 2. 5 V reference. Will the output be linear over the full 0 V to 1 V signal range? Analog engineer’s calculator used to select U 2 Feedback resistors 8

Quiz: Linear Range ADC + FDA Problem 2: continued. PARAMETER OPA 320 INPUT VOLTAGE Common-mode voltage range OUTPUT Voltage swing from both rails TEST CONDITION Vcm VO MIN TYP MAX (V+)+0. 1 (V-) - 0. 1 RL = 10 kΩ 10 20 RL = 2 kΩ 25 35 UNIT V m. V OPEN-LOOP GAIN Open-loop gain Amplifier input range Amplifier output range Amplifier Linear Range Worst Case Range AOL 0. 1 < Vo < (V+)-0. 1 V, RL = 10 kΩ 0. 2 < Vo < (V+)-0. 2 V, RL = 2 kΩ 114 108 132 123 d. B -2. 6 V < Vcm < 2. 6 V -2. 48 < VO < 2. 48 V -2. 4 < VO < 2. 4 V 9

Quiz: Linear Range ADC + FDA Problem 2: continued. PARAMETER THS 4551 MIN Output voltage low Output voltage high (V+) – 0. 23 (V+) – 1. 2 MAX (V-) + 0. 23 (V+) – 0. 2 (V-) + 0. 2 Common mode input voltage low Common mode input voltage high TYP (V-) + 0. 2 (V+) – 1. 1 UNIT V V (V-) – 0. 1 V input range output range -0. 1 V < Vcm < 3. 8 V 0. 23 < VO < 4. 77 V V 10

Quiz: Linear Range ADC + FDA Problem 2: continued. Note: One approach to avoiding the output swing limitation is a -0. 3 V negative supply. 11

Quiz: Linear Range ADC + FDA 3. (False) Assume the input signal applied to an FDA has both even and odd order harmonics. The the FDA will cancel the even order harmonics. 4. (False) The Vocm pin can be directly connected to a voltage divider to set it’s output common mode. 12