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ADC-207 Fiches technique(PDF) 3 Page - Murata Power Solutions Inc. |
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ADC-207 Fiches technique(HTML) 3 Page - Murata Power Solutions Inc. |
3 / 6 page OUTPUT CODING (+REFERENCE = +5.12V, –REFERENCE = ground, MIDPOINT = no connection) NOTE: The reference should be held to ±0.1% accuracy or better. Do not use the +5V power supply as a reference input without precision regulation and high frequency decoupling. Values shown here are for a +5.12V reference. Scale other references proportionally. Calibration equipment should test for code changes at the midpoints between these center values shown in Table 1. For example, at the half-scale major carry, set the input to 2.54V and adjust the reference until the code flickers equally between 63 and 64. Note also that the weighting for the comparator resistor network leaves the first and last thresholds within 1/2LSB of the end points to adjust the code transition to the proper midpoint values. buffer has two enable lines, CS1 and CS2. Table 2 shows the truth table for chip select signals. CS1 has the function of enabling/disabling bits 1 through 7. CS2 has the function of enabling/disabling bits 1 through 7 and the overflow bit. Also, a full-scale input produces all ones, including the overflow bit at the output. The ADC-207 has an adjustable resistor ladder string. The top end, idle point, and bottom end are brought out for use with applications circuits. These pins are called +REFERENCE, MIDPOINT and –REFERENCE, respectively. In typical operation +REFERENCE is tied to +5V, –REFERENCE is tied to ground, and MIDPOINT is bypassed to ground. Such a configura- tion results in a 0 to +5V input voltage range. The MIDPOINT pin can also be tied to a +2.5V source to further improve integral linearity. This is usually not necessary unless better than 7-bit linearity is needed. ADC-207 OPERATION The ADC-207 uses a switched capacitor scheme in which there is an auto- zero phase and a sampling phase. See Figure 1 and Timing Diagram. The ADC-207 uses a single clock input. When the clock is at a high state (logic 1), the ADC-207 is in the auto-zero phase (Ø1). When the clock is at a low state (logic 0), the ADC-207 is in the sampling phase (Ø2). During phase 1, the 128 comparator outputs are shorted to their inputs through CMOS switches. This serves the purpose of bringing the inputs and outputs to the transition levels of the respective comparators. The inputs to the comparators are also connected to 128 sampling capacitors. The other end of the 128 capacitors are also shorted to 128 taps of a resistor ladder, via CMOS switches. Therefore, during phase 1 the sampling capacitors are charged to the differential voltage between a resistor tap and its respective comparator transition voltage. This eliminates offset differences between comparators and yields better temperature performance. During phase 2 (Ø2) the input voltage is applied to the 128 capacitors, via CMOS switches. This forces the comparators to trip either high or low. Since the comparators during phase 1 were sitting at their transition point, they can trip very quickly to the correct state. Also during phase 2, the outputs of the comparators are loaded into internal latches which in turn feed a128-to-7 encoder. When going back into phase 1, the output of the encoder is loaded into an output latch. This latch then feeds the 3-state output buffer. This means that the ADC-207 is of pipeline design. To do a single conversion, the ADC-207 requires a positive pulse followed by a negative pulse followed by a positive pulse. Continuous conversion requires one cycle/sample (one positive pulse and one negative pulse). The 3-state CLOCK OUTPUT DATA AUTO ZERO N DATA N+1 DATA SAMPLE N SAMPLE N + 1 SAMPLE N + 2 AUTO ZERO AUTO ZERO 17ns max. 17ns max. Æ1 Æ2 Æ1 Æ1 Æ2 Æ2 TIMING DIAGRAM Analog Input (Center Value) Code Overflow 1234567 Decimal Hexadecimal (Incl. 0V) MSB LSB 0.00V Zero 0 0000000 0 00 +0.04V +1LSB 0 0000001 1 01 +1.28V +1/4FS 0 0100000 32 20 +2.52V +1/2FS – 1LSB 0 0111111 63 3F +2.56V +1/2FS 0 1000000 64 40 +2.60V +1/2FS + 1LSB 0 1000001 65 41 +3.84V +3/4FS 0 1100000 96 60 +5.08V +FS 0 1111111 127 7F +5.12V Overflow 1 1111111 255* FF *Note that the overflow code does not clear the data bits. Table 1. ADC-207 Output Coding Table 2. Chip Select Truth Table CS1 CS2 Bits 1-7 Overflow Bit 0 0 3-State Mode 3-State Mode 1 0 3-State Mode 3-State Mode 0 1 Data Outputed Data Outputed 1 1 3-State Mode Data Outputed NOTE: Reduce the sample time (sample pulse) to 12ns to improve performance above 20MHz. Such a configuration will closely resemble an ideal sampler. ADC-207 7-Bit, 20MHz, CMOS Flash A/D Converters MDA_ADC-207.B01 Page 3 of 6 Technical enquiries email: sales@murata-ps.com, tel: +1 508 339 3000 www.murata-ps.com |
Numéro de pièce similaire - ADC-207 |
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Description similaire - ADC-207 |
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