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AN642 Dataheets PDF



Part Number AN642
Manufacturers Maxim Integrated Products
Logo Maxim Integrated Products
Description Analog-to-Digital Converter Captures 1Gsps
Datasheet AN642 DatasheetAN642 Datasheet (PDF)

A/D and D/A CONVERSION/SAMPLING CIRCUITS HIGH-SPEED SIGNAL PROCESSING Application Note 642: Jan 22, 2001 Analog-to-Digital Converter Captures 1Gsps One of the industry's first ultra high-speed, 8-bit data converters with highest AC performance and a GHz input bandwidth, the MAX104/6/8 family of data converters offers both sampling speed and signal bandwidth for applications where these parameters are of the utmost importance. At their introduction in 1999, this family of high-speed analog-to-d.

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A/D and D/A CONVERSION/SAMPLING CIRCUITS HIGH-SPEED SIGNAL PROCESSING Application Note 642: Jan 22, 2001 Analog-to-Digital Converter Captures 1Gsps One of the industry's first ultra high-speed, 8-bit data converters with highest AC performance and a GHz input bandwidth, the MAX104/6/8 family of data converters offers both sampling speed and signal bandwidth for applications where these parameters are of the utmost importance. At their introduction in 1999, this family of high-speed analog-to-digital converters (ADCs) set a new standard for dynamic performance requirements in high-frequency, wide-bandwidth applications. The following article outlines the advantages of this family of ADCs and describes their impact and importance on digital communications, DSOs and fast data acquisition systems. The MAX104 processes analog input bandwidths that exceed 2.2GHz with 8-bit resolution. It sets a new standard for performance in high-frequency, high-bandwidth digital communications receivers, digital oscilloscopes, and high-speed data-acquisition systems. The MAX104 is a fast silicon monolithic analog-to-digital converter (ADC) that integrates a highbandwidth track/hold (T/H) amplifier (Figure 1) with a high-speed quantizer that supports accurate digitizing of wideband analog input signals from DC to 2.2GHz. It is based on Maxim's GST-2 Giga-Speed silicon-bipolar process technology. This high-speed, self-aligned double-polysilicon process has been developed for high-density, high-performance circuits. It employs many of the features, such as trench isolation, that are incorporated in Maxim's lower performance GST-1 process. Figure 1. This simplified block diagram shows how the MAX104 integrates a high-bandwidth T/H amplifier with a high-speed quantizer. Although many of the outstanding performance parameters of the MAX104 are possible with the integrated-circuit process (such as a transition frequency of 27GHz for NPN transistors, a three-metal interconnect system, small geometry, and precision laser-trimmed nickel-chrome (NiCr) thin-film www.maxim-ic.com/an642 Page 1 of 7 resistors), additional credit goes to the MAX104's design team for creating an efficient and effective ADC architecture. Most high-speed ADCs that sample more than several hundred megahertz have input bandwidths that are limited to no more than their maximum sampling frequency to improve noise performance. One example is the signal-to-noise ratio (SNR). This limited input bandwidth may rule out use in applications where bandwidths of interest in the input spectrum are higher, and an undersampling approach is needed. Also, if the input signal is changing rapidly during conversion, the effective number of bits (ENOB) and SNR will be reduced. The MAX104's on-chip 2.2GHz full-power-bandwidth T/H amplifier (Figure 2) increases dynamic performance significantly and supports more precise capture of fast analog data at extremely high conversion rates. Figure 2. The MAX104's full-power bandwidth is shown as a function of input amplitude. Bandgap reference The MAX104 features an on-board +2.5V precision bandgap reference, which can be activated by connecting the bandgap reference's output contact (REFOUT) to the in-phase input (REFIN) of the internal reference amplifier. The negative input of this amplifier is internally tied to the reference ground (GNDR). The REFOUT port can provide a current of up to 2.5mA for external devices. This is enough drive for two MAX104s configured for interleaved operation (to achieve a sampling rate of 2 gigasamples per second, or 2Gsps). Since the bandgap reference source is internally compensated, external bypass components are not needed with REFOUT connections. To overdrive the internal reference, an external precision reference can be connected to the REFIN pin with REFOUT left floating. The external reference may then be used to adjust the full-scale range of the MAX104. The MAX104's T/H amplifier input circuit design reduces the input signal requirement and supports a fullscale signal input range of 500mV peak-to-peak. Obtaining a full-scale digital output with a differential input requires 250mV applied between the positive (VIN+) and the negative input (VIN-) pins. Midscale digital output codes occur at an input of 0V. For a zero-scale digital output code, the negative input (VIN-) must be 250mV above the positive input (VIN+). The high-performance differential T/H amplifier enables the MAX104 to be used in single-ended input configurations without any degradation in dynamic performance. For a typical single-ended configuration, the analog input signal is coupled to the T/H amplifier stage at the in-phase input pad (VIN+), while the inverted phase input (VIN-) pad is referenced to ground. Single-ended operation supports an input amplitude of 500mV peak-to-peak, centered at approximately 0V. For minimizing www.maxim-ic.com/an642 Page 2 of 7 reflections and improving performance, the MAX104 inputs feature imped.


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