Linear Technology introduced the LTM9012, a quad 14-bit, 125 MSps μModule analog-to-digital converter (ADC) with integrated fixed gain drivers, passive filtering and bypass capacitance. The integrated μModule converters offer reduction in board space for high channel-count applications as diverse as medical imaging systems and MIMO (multiple input multiple output) 4G base stations.
Integrating the driver with the ADC simplifies high-speed design, whether the signal originates in an image sensor with CMOS logic outputs or an RF signal chain. CMOS image sensors are used in high-end medical instruments, such as blood cell or molecular microscope cameras, and industrial imaging equipment used for detecting voids in metal objects.
Depending on the sensor, many channels of high-speed digitisers are required along with filtering and amplification to translate the sensor output to the ADC input. Filters and amplifiers often consume more than twice the circuit board area as the ADC itself and constitute the key challenge in achieving maximum camera resolution. The LTM9012 amplifiers easily accommodate the single-ended CMOS sensor outputs and translate these levels to differential for the high-performance ADC to maximise dynamic range.
The device also excels in baseband receiver applications such as cellular infrastructure. Two receiver architectures dominate base station designs: direct conversion and IF-sampling. With the capability of supporting baseband frequencies up to about 90 MHz, the LTM9012 is suitable for both types.
Direct conversion demodulates the RF signal and down-converts to DC; therefore a 20 MHz low-pass filter supports 40 MHz signal bandwidth. Low IF-sampling below 90 MHz is also possible with four channels for next generation small base station designs. With 20 dB of gain, the LTM9012 achieves 68,3 dB signal to noise ratio (SNR) and 78 dB spurious-free dynamic range (SFDR).
Compared to previous generation devices (LTM9002), the LTM9012 offers many enhancements. It has twice the density – two channels versus four in the same package size. It requires only a third of the number of digital data lines since it utilises serial LVDS. It consumes about one fourth of the power, just 318 mW per channel, operating on 1,8 V for the ADC core and 3,3 V for the amplifiers.
The IC is packaged in a space-saving 15 x 11,25 mm BGA package, utilising a multilayer substrate that shields sensitive analog lines from the digital traces to minimise digital feedback. Supply and reference bypass capacitance is placed inside the module, tightly coupled to the die, providing a space, cost and performance advantage over traditional packaging.
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