Datasheet LTC1420 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | 12-Bit, 10Msps, Sampling ADC |
| Pages / Page | 20 / 10 — APPLICATIONS INFORMATION Table 2. Comparison of Analog Input … |
| File Format / Size | PDF / 257 Kb |
| Document Language | English |
APPLICATIONS INFORMATION Table 2. Comparison of Analog Input Configurations. SUPPLIES. COUPLING. REF. GAIN. AIN. COMMENTS
Model Line for this Datasheet
Text Version of Document
LTC1420
U U W U APPLICATIONS INFORMATION Table 2. Comparison of Analog Input Configurations SUPPLIES COUPLING V + – REF GAIN AIN AIN COMMENTS
±5V DC 4.096V 1× ±2.048 0 Best SNR, THD 5V DC 4.096V 2× 2.5 ± 1.024 2.5 Best SINAD, THD for Single Supply 5V DC 2.048V 1× 2.5 ± 1.024 2.5 Worse Noise than Above Case 5V DC 4.096V 1× 2.5 ± 2.048 2.5 Best Single Supply Noise, THD Is Not Optimal 5V DC 4.096V 1× 0 to 4.096 2.048 Same As Above ±5V AC 4.096V 1× ±1.024 ±1.024 Very Best SNR, THD (Transformer) 5V AC 4.096V 1× 2.5 ± 1.024 2.5 ± 1.024 Very Best SNR, THD for Single Supply (Transformer) 5V
DC Coupling the Input
4.096V In most applications the analog input signal can be directly V +A IN IN coupled to the LTC1420 inputs. If the input signal is 0V LTC1420 2.048V centered around ground, such as when dual supply op 5V –AIN amps are used, simply connect – AIN to ground and SENSE connect VSS to –5V (Figure 4). In a single power supply VSS system with the input signal centered around 2.5V, con- 1420 F06 nect – AIN to VCM and VSS to ground (Figure 5). If the input signal is not centered around ground or 2.5V, the voltage
Figure 6. DC Coupling a 0V to 4.096V Signal
for – AIN must be generated externally by a resistor divider or a voltage reference (Figure 6).
AC Coupling the Input
5V The analog inputs to the LTC1420 can also be AC coupled 0V V +A through a capacitor, though in most cases it is simpler to IN IN LTC1420 directly couple the input to the ADC. Figure 7 shows an –AIN example where the input signal is centered around ground and the ADC operates from a single 5V supply. Note that VCM V the performance would improve if the ADC was operated SS 1µF 1420 F04 from a dual supply and the input was directly coupled (as –5V in Figure 4). With AC coupling the DC resistance to ground
Figure 4. DC Coupling a Ground
should be roughly matched for + AIN and – AIN to maintain
Centered Signal (Dual Supply System)
offset accuracy. 5V 5V C 2.5V V +A IN IN 0V V +A IN IN LTC1420 LTC1420 –AIN –AIN C R R VCM V V CM SS VSS 1µF 1µF 1420 F05 1420 F07
Figure 5. DC Coupling a Signal Centered Figure 7. AC Coupling to the LTC1420. Note That the Input Signal Around 2.5V (Single Supply System) Can Almost Always Be Directly Coupled with Better Performance
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U U W U APPLICATIONS INFORMATION Table 2. Comparison of Analog Input Configurations SUPPLIES COUPLING V + – REF GAIN AIN AIN COMMENTS
±5V DC 4.096V 1× ±2.048 0 Best SNR, THD 5V DC 4.096V 2× 2.5 ± 1.024 2.5 Best SINAD, THD for Single Supply 5V DC 2.048V 1× 2.5 ± 1.024 2.5 Worse Noise than Above Case 5V DC 4.096V 1× 2.5 ± 2.048 2.5 Best Single Supply Noise, THD Is Not Optimal 5V DC 4.096V 1× 0 to 4.096 2.048 Same As Above ±5V AC 4.096V 1× ±1.024 ±1.024 Very Best SNR, THD (Transformer) 5V AC 4.096V 1× 2.5 ± 1.024 2.5 ± 1.024 Very Best SNR, THD for Single Supply (Transformer) 5V
DC Coupling the Input
4.096V In most applications the analog input signal can be directly V +A IN IN coupled to the LTC1420 inputs. If the input signal is 0V LTC1420 2.048V centered around ground, such as when dual supply op 5V –AIN amps are used, simply connect – AIN to ground and SENSE connect VSS to –5V (Figure 4). In a single power supply VSS system with the input signal centered around 2.5V, con- 1420 F06 nect – AIN to VCM and VSS to ground (Figure 5). If the input signal is not centered around ground or 2.5V, the voltage
Figure 6. DC Coupling a 0V to 4.096V Signal
for – AIN must be generated externally by a resistor divider or a voltage reference (Figure 6).
AC Coupling the Input
5V The analog inputs to the LTC1420 can also be AC coupled 0V V +A through a capacitor, though in most cases it is simpler to IN IN LTC1420 directly couple the input to the ADC. Figure 7 shows an –AIN example where the input signal is centered around ground and the ADC operates from a single 5V supply. Note that VCM V the performance would improve if the ADC was operated SS 1µF 1420 F04 from a dual supply and the input was directly coupled (as –5V in Figure 4). With AC coupling the DC resistance to ground
Figure 4. DC Coupling a Ground
should be roughly matched for + AIN and – AIN to maintain
Centered Signal (Dual Supply System)
offset accuracy. 5V 5V C 2.5V V +A IN IN 0V V +A IN IN LTC1420 LTC1420 –AIN –AIN C R R VCM V V CM SS VSS 1µF 1µF 1420 F05 1420 F07
Figure 5. DC Coupling a Signal Centered Figure 7. AC Coupling to the LTC1420. Note That the Input Signal Around 2.5V (Single Supply System) Can Almost Always Be Directly Coupled with Better Performance
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