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DESIGN IDEA
Amplifier Closed-Loop Bandwidth Considerations in High Resolution A/D Converter Applications
Jerry Freeman, Applications Engineer
Amplifier Bandwidth Limitations Amplifier closed-loop bandwidth-limited accuracy considerations are critical when driving high resolution A/D Converters (ADCs). It is useful to be able to predict, for any closed loop gain, the required gain-bandwidth (GBW) product of an op amp to achieve a specified level of accuracy in terms of the minimum ADC resolution. Other sources of error include offset, noise, and distortion, which are beyond the scope of this article. A simple equation will be developed below that relates the minimum closed-loop bandwidth of an op amp to the resolution requirements of a given ADC.
Download (pdf 346KB)
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Single/Dual, High Precision, Rail-to-Rail Output Operational Amplifier
The LMP2011/12/14 (single/dual/quad) are part of the LMP™ family of precision amplifiers that offer an industry leading gain bandwidth of 3 MHz, while maintaining high precision and low drift over time. These amplifiers deliver excellent CMRR (130 dB) and PSRR (120 dB) ratings without frequency related noise (no 1/f). The high CMRR allows for high accuracy across voltages.
The LMP2011/12/14 deliver a very low input offset voltage which offers high accuracy measurements with continued accuracy over temperature. The low voltage noise increases signal accuracy during low frequency measurements. No external capacitors are required.
Features
- Low guaranteed VOS over temperature 60 µV
- Low noise with no 1/f , 35 nV/√Hz
- High CMRR 130 dB
- High PSRR 120 dB
- High AVOL 130 dB
- Wide gain-bandwidth product 3 MHz
- High slew rate 4 V/µs
- Low supply current 930 µA
- Rail-to-rail output 30 mV from rails
The extended temperature range of -40ºC to 125ºC allows for operation in demanding industrial and automotive applications, as well as in precision instrumentation amplifiers, thermocouple amplifiers, and strain gauge bridge amplifiers. The LMP2011 is offered in SOIC-8 and SOT23-5 packaging. The LMP2012 is offered in SOIC-8 and mini SOIC-8 packaging. The LMP2014 is offered in TSSOP-14 packaging.
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Low Power, 200 kSPS to 500 kSPS, 8/10/12-Bit A/D Converters
The ADC081S051, ADC101S051, and ADC121S051 are lowpower, single channel, CMOS 8/10/12-bit Analog-to-Digital Converters (ADCs) with a high-speed serial interface. Unlike the conventional practice of specifying performance at a single sample rate only, these ADCs are fully specified over a sample rate range of 200 kSPS to 500 kSPS.
Operation with a single supply can range from +2.7V to +5.25V. Normal power consumption for the ADC121S051 using a +3.6V or +5.25V supply is 1.7 mW and 8.7 mW, respectively. The power-down feature reduces the power consumption to as low as 2.6 µW using a +5.25V supply.
Features
- Speed range: 200 kSPS to 500 kSPS
- Integral Non-Linearity (INL):
- +0.45, -0.40 LSB (ADC121S051)
- +0.15, -0.09 LSB (ADC101S051)
- +0.06, -0.05 LSB (ADC081S051)
- Differential Non-Linearity (DNL):
- +0.5, -0.25 LSB (ADC121S051)
- +0.15, -0.11 LSB (ADC101S051
- +0.06, -0.045 LSB (ADC081S051)
- Signal-to-Noise Ratio (SNR):
- 72.0 dB (ADC121S051)
- 61.6 dB (ADC101S051)
- 49.6 dB (ADC081S051)
The ADC081S051, ADC101S051, and ADC121S051 are ideal for use in applications including portable systems, remote data acquisitions, and instrumentation and control systems. These low power ADCs are offered in LLP-6 and SOT23-6 packaging.
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Low Power, High Precision 8/10/12-Bit, 1 MSPS A/D Converters
The ADC081S101, ADC101S101, and ADC121S101 are lowpower, single channel, CMOS 8/10/12-bit Analog-to-Digital Converters (ADCs) with a high-speed serial interface. Operation with a single supply can range from +2.7V to +5.25V. Normal power consumption using a +3V or +5V supply is 2 mW and 10 mW, respectively. The power-down feature reduces the power consumption to as low as 2.5 µW using a +5V supply.
Features
- Speed range: 500 kSPS to 1 MSPS
- Integral Non-Linearity (INL):
- ±0.4 LSB (ADC121S101)
- ±0.2 LSB (ADC101S101)
- ±0.05 LSB (ADC081S101)
- Differential Non-Linearity (DNL):
- +0.5, -0.3 LSB (ADC121S101)
- +0.3, -0.2 LSB (ADC101S101)
- ±0.07 LSB (ADC081S101)
- Signal-to-Noise Ratio (SNR):
- 72.5 dB (ADC121S101)
- 62 dB (ADC101S101)
- 49.7 dB (ADC081S101)
The ADC081S101, ADC101S101, and ADC121S101 are ideal for use in applications including portable systems, remote data acquisitions, instrumentation, and control systems. These ADCs are offered LLP-6 and SOT23-6 packaging.
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Precision, 17 MHz, Low Noise, CMOS Input Op Amps
The LMP7711/12 (single/dual) are low-noise, low offset, CMOS input, rail-to-rail output precision amplifiers with a high gain bandwidth and an enable pin. These precision amplifiers achieve an input bias current of 100 fA, an input referred voltage noise of 5.8 nV/√Hz and an input offset voltage of less than ±150 µV, using a CMOS input stage.
These features make the LMP7711/12 superior choices for precision applications. Consuming only 1.15 mA of supply current, the LMP7711 offers a high gain bandwidth product of 17 MHz, enabling accurate amplification at high closed loop gains. The high PSRR (100 dB) and CMRR (100 dB) ensure high accuracy with noisy supplies, and high accuracy over a wide input range.
Features
- ±150 µV (max) input offset voltage
- 100 fA input bias current
- 5.8 nV/√Hz input voltage noise
- 17 MHz gain bandwidth product
- 1.15 mA supply current (LMP7711)
- 1.30 mA supply current (LMP7712)
- 0.001% THD+N at f = 1 kHz
Rail-to-rail output swing Operating at -40°C to +125°C, these precision amplifiers are ideal for use in sensor interface applications, transimpedance amplifiers, and active filters and buffers. The LMP7711 is offered in Thin SOT23-6 packaging and the LMP7712 is offered in a MSOP-10 packaging.
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