REPLACING INTEGRATORS WITH RESONATORS GIVES A BANDPASS SIGMA-DELTA ADC CLOCK KIs ANALOG DIGITAL Figure 3. 13 A Sigma-Delta ADC works by over-sampling, where simple analog filters in the Sigma-Delta modulator shape the quantization noise so that the snr in the bandwidth of interest is much lower than would otherwise be the case, and by using circuitry of the digital filter. Because the basic ADC is 1-bit(a comparator), the Ro# high performance digital filters and decimation to eliminate noise outside the required passband. Because the analog circuitry is so simple and undemanding may be built with the same digital vlsi process that is used to fabricate the dsi technique is inherently linear Although the detailed analysis of Sigma-Delta ADCs involves quite complex mathematics, their basic design can be understood without the necessity of any mathematics at all. For further discussion on Sigma-Delta ADCs, refer to References 2 and 3 SIGMA-DELTA SUMMARY Linearity is Inherently Excellent High Resolutions(16-24 Bits) Ideal for Mixed-signal IC Processes, no Trimming No SHA Required Charge Injection at Input Presents Drive Problems Upper Sampling Rate Currently Limits Applications to Measurement, Voiceband, and Audio, but Bandpass Sigma-Delta Techniques Will Change This Analog Multiplexing Applications are Limited by nternal Filter Settling Time. Consider One Sigma Delta ADC per Channel Figure 3.14
1 1 REPLACING INTEGRATORS WITH RESONATORS GIVES A BANDPASS SIGMA-DELTA ADC Figure 3.13 A Sigma-Delta ADC works by over-sampling, where simple analog filters in the Sigma-Delta modulator shape the quantization noise so that the SNR in the bandwidth of interest is much lower than would otherwise be the case, and by using high performance digital filters and decimation to eliminate noise outside the required passband. Because the analog circuitry is so simple and undemanding, it may be built with the same digital VLSI process that is used to fabricate the DSP circuitry of the digital filter. Because the basic ADC is 1-bit (a comparator), the technique is inherently linear. Although the detailed analysis of Sigma-Delta ADCs involves quite complex mathematics, their basic design can be understood without the necessity of any mathematics at all. For further discussion on Sigma-Delta ADCs, refer to References 2 and 3. SIGMA-DELTA SUMMARY Linearity is Inherently Excellent High Resolutions (16 - 24 Bits) Ideal for Mixed-Signal IC Processes, no Trimming No SHA Required Charge Injection at Input Presents Drive Problems Upper Sampling Rate Currently Limits Applications to Measurement, Voiceband, and Audio, but Bandpass Sigma-Delta Techniques Will Change This Analog Multiplexing Applications are Limited by Internal Filter Settling Time. Consider One SigmaDelta ADC per Channel. Figure 3.14
HIGH RESOLUTION, LOW-FREQUENCY MEASUREMENT ADCs The AD7710, AD7711, AD7712, AD7713, and AD7714 are members of a family of sigma-delta converters designed for high accuracy, low frequency measurements. They have no missing codes at 24-bits and useful resolution of up to 21.5-bits (AD7710, AD7711, AD7712, and AD7713), and 22.5 bits(AD7714). They all use similar sigma-delta cores, and their main differences are in their analog inputs which are optimized for different transducers. The AD7714 is the newest member of the family and is fully specified for either +5V(AD7714-5)or +3V(AD7714-3) operation The digital filter in the sigma-delta core may be programmed by the user for output update rates between 10Hz and 1kHz(AD7710, AD7711, AD7712), 2Hz and 200Hz (AD7713), and 2Hz and 1kHz(AD7714). The effective resolution of these ADCs is inversely proportional to the bandwidth. For example, for 22 5-bits of effective resolution, the output update rate of the AD7714 cannot exceed 10Hz. The AD771X family is ideal for such sensor applications as those shown in Figure 3.15 SIGNAL CONDITIONING TRANSDUCER INPUT ADCs THE AD7710,AD7711,AD7712,AD7713,AD7714 Ultra-High Resolution Measurement Systems Implemented Using 2A Conversion Ideal for Applications Such As: Weigh Scales RTDS Thermocouples Strain Gauges Process Control Smart Transmitters Medical Figure 3.15 The AD771X family has a high level of integration which simplifies the design of data acquisition systems. For example, the AD7710(Figures 3. 16 and 3. 17) has two high impedance differential inputs that can be interfaced directly to many different sensors, including resistive bridges. The two inputs are selected by the internal PGA has a digitally programmable gain range of 1 to 128 to accommodate a wide o multiplexer, which passes the signal to a programmable gain amplifier(PGa). Th range of signal inputs. After the PGa, the signal is digitized by the sigma-delta modulator. The digital filter notch frequency may be adjusted from 10Hz to 1kHz, which allows various input bandwidths To achieve this high accuracy the ad771X family has four different internal calibration modes, including system and background calibration. All of these
1 2 HIGH RESOLUTION, LOW-FREQUENCY MEASUREMENT ADCS The AD7710, AD7711, AD7712, AD7713, and AD7714 are members of a family of sigma-delta converters designed for high accuracy, low frequency measurements. They have no missing codes at 24-bits and useful resolution of up to 21.5-bits (AD7710, AD7711, AD7712, and AD7713), and 22.5 bits (AD7714). They all use similar sigma-delta cores, and their main differences are in their analog inputs, which are optimized for different transducers. The AD7714 is the newest member of the family and is fully specified for either +5V (AD7714-5) or +3V (AD7714-3) operation. The digital filter in the sigma-delta core may be programmed by the user for output update rates between 10Hz and 1kHz (AD7710, AD7711, AD7712), 2Hz and 200Hz (AD7713), and 2Hz and 1kHz (AD7714). The effective resolution of these ADCs is inversely proportional to the bandwidth. For example, for 22.5-bits of effective resolution, the output update rate of the AD7714 cannot exceed 10Hz. The AD771X family is ideal for such sensor applications as those shown in Figure 3.15. SIGNAL CONDITIONING, TRANSDUCER INPUT ADCs THE AD7710, AD7711, AD7712, AD7713, AD7714 Ultra-High Resolution Measurement Systems Implemented Using Conversion Ideal for Applications Such As: Weigh Scales RTDs Thermocouples Strain Gauges Process Control Smart Transmitters Medical Figure 3.15 The AD771X family has a high level of integration which simplifies the design of data acquisition systems. For example, the AD7710 (Figures 3.16 and 3.17) has two high impedance differential inputs that can be interfaced directly to many different sensors, including resistive bridges. The two inputs are selected by the internal multiplexer, which passes the signal to a programmable gain amplifier (PGA). The PGA has a digitally programmable gain range of 1 to 128 to accommodate a wide range of signal inputs. After the PGA, the signal is digitized by the sigma-delta modulator. The digital filter notch frequency may be adjusted from 10Hz to 1kHz, which allows various input bandwidths. To achieve this high accuracy, the AD771X family has four different internal calibration modes, including system and background calibration. All of these
functions are controlled via a serial interface, a benefit of this serial interface is that the aD771X-family fits into a 24-pin package giving a small footprint for the high level of integration. All of the parts except the AD7713 and AD7714 can operate on either a single +5V or dual +5 V supplies. The AD7713 is designed exclusively for single supply (+5V)operation. The AD7714 is the newest member of the family and is designed for either single +3V(AD7714-3)or single +5V(AD7714-5) low power applications. The AD771X family has <0.0015% non-linearit THE AD77IX-SERIES PROVIDES A HIGH LEVEL OF INTEGRATION IN A 24-PIN PACKAGE EF REF REF OUT 2.5V REFERENCE 女 CHARGING BALANCING AD CONVERTER AIN1() AUTO· ZEROED DIGITAL O SYNC FILTER x.MODULATOR CLOCK GENERATION MCLK SERIAL INTERFACE CONTHOL OUTPUT REGISTER REGISTER AD7710 AGND DGND Vss RFS TFS MODE SDATA SCLK DRD 3.16 KEY FEATURES OF THE AD7710 ■±0.0015% Nonlinearity Two Channels with Differential Inputs Programmable Gain Amplifier (G=1 to 128) Programmable Low Pass Filter System or Self-Calibration Options Single or Dual 5V Supply Operation Microcontroller serial Interface Figure 3. 17
1 3 functions are controlled via a serial interface. A benefit of this serial interface is that the AD771X-family fits into a 24-pin package, giving a small footprint for the high level of integration. All of the parts except the AD7713 and AD7714 can operate on either a single +5V or dual ±5V supplies. The AD7713 is designed exclusively for single supply (+5V) operation. The AD7714 is the newest member of the family and is designed for either single +3V (AD7714-3) or single +5V (AD7714-5) low power applications. The AD771X family has <0.0015% non-linearity. THE AD771X-SERIES PROVIDES A HIGH LEVEL OF INTEGRATION IN A 24-PIN PACKAGE Figure 3.16 KEY FEATURES OF THE AD7710 0.0015% Nonlinearity Two Channels with Differential Inputs Programmable Gain Amplifier (G = 1 to 128) Programmable Low Pass Filter System or Self-Calibration Options Single or Dual 5V Supply Operation Microcontroller Serial Interface Figure 3.17
The AD7710, AD7711, AD7712, and AD7713 have identical structures of PGA, sigma-delta modulator, and serial interface. Their main differences are in their input configurations. The AD7710 has two low level differential inputs, the AD7711 two low level differential inputs with excitation current sources which make it idea for RTD applications, the AD7712 has one low level differential input and a single ended high level input that can accommodate signals of up to four times the reference voltage, and the AD7713 is designed for loop-powered applications where power dissipation is important. The AD7713 consumes only 3.5mw of power from a single ly The AD7714 is designed for either +3V(AD7714-3)or +5V(AD7714-5)single-supply, low power applications. It has a buffer between the multiplexer and the Pga which can be enabled or bypassed using a control line. When the buffer is active, it isolates the analog inputs from the transient currents and variable impedance of the switched-capacitor PGA SUMMARY TABLE OF AD771X DIFFERENCES AD7710: 2-Channel Low-Level differential Inputs AD7711: o 1-Channel Low-Level Differential Input 1-Channel Low-Level Single-Ended Input Excitation Current sources for 3 or 4-Wire rtDs AD7712: o 1-Channel Low-Level Differential Input o 1-Channel High-Level Single-Ended Input AD7713: 2-Channel Low-Level Differential Inputs 1-Channel High-Level Single-Ended Input Excitation Current sources for 3 or 4-Wire rtDs o Single 5V Operation Only Low Power(.5mW) No Internal Reference AD7714: o 3-Channel Low-Level Differential Inputs or 5 Channel Pseudo-Differential Inputs o Single +3V(AD7714-3)or Single +5V(AD7714-5) Low Power (1.5mW: AD7714-3) No internal reference Figure 3. 18 Because of the differences in analog interfaces, each device is best suited to a particular sensor or system application. In other words, the sensor and the system requirements (i.e. type of sensor, single versus dual supply, power consumption, etc determine which converter should be used. Figure 3. 19 lists the converters, and the sensors and applications to which they are best suited
1 4 The AD7710, AD7711, AD7712, and AD7713 have identical structures of PGA, sigma-delta modulator, and serial interface. Their main differences are in their input configurations. The AD7710 has two low level differential inputs, the AD7711 two low level differential inputs with excitation current sources which make it ideal for RTD applications, the AD7712 has one low level differential input and a single ended high level input that can accommodate signals of up to four times the reference voltage, and the AD7713 is designed for loop-powered applications where power dissipation is important. The AD7713 consumes only 3.5mW of power from a single +5V supply. The AD7714 is designed for either +3V (AD7714-3) or +5V (AD7714-5) single-supply, low power applications. It has a buffer between the multiplexer and the PGA which can be enabled or bypassed using a control line. When the buffer is active, it isolates the analog inputs from the transient currents and variable impedance of the switched-capacitor PGA. SUMMARY TABLE OF AD771X DIFFERENCES AD7710: 2-Channel Low-Level Differential Inputs AD7711: 1-Channel Low-Level Differential Input 1-Channel Low-Level Single-Ended Input Excitation Current Sources for 3 or 4-Wire RTDs AD7712: 1-Channel Low-Level Differential Input 1-Channel High-Level Single-Ended Input AD7713: 2-Channel Low-Level Differential Inputs 1-Channel High-Level Single-Ended Input Excitation Current Sources for 3 or 4-Wire RTDs Single 5V Operation Only Low Power (3.5mW) No Internal Reference AD7714: 3-Channel Low-Level Differential Inputs or 5- Channel Pseudo-Differential Inputs Single +3V (AD7714-3) or Single +5V (AD7714-5) Low Power (1.5mW: AD7714-3) No Internal Reference Figure 3.18 Because of the differences in analog interfaces, each device is best suited to a particular sensor or system application. In other words, the sensor and the system requirements (i.e. type of sensor, single versus dual supply, power consumption, etc.) determine which converter should be used. Figure 3.19 lists the converters, and the sensors and applications to which they are best suited