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ML2713CH Folha de dados(PDF) 8 Page - Micro Linear Corporation |
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ML2713CH Folha de dados(HTML) 8 Page - Micro Linear Corporation |
8 / 18 page ML2713 8 January, 2000 PRELIMINARY DATASHEET PRELIMINARY OPERATIONAL MODES MODE CONTROL The ML2713 has four modes of operation; 1) Filer Align, 2) Transmit, 3) Receive, and 4) Sleep. The operating modes of the ML2713 are programmed through the parallel interface made up of pins RS, TS, and LOE. These pins dynamically control the mode, and will enable the appropriate circuitry within 1msec of transitioning low. These control pins have on chip pull ups to VCC1, and are CMOS compatible. The relationship between the operating modes and control pins is shown in Table 1. S RS TE O Ln o i t a r e p O f o e d o M h g i Hh g i Hh g i He d o M p e e l S h g i Hh g i Hw o L n g i l A r e t l i F s t i u c r i C r e v i e c e R e m o S r e t l i F o t u A , d e l b a n E n O t n e m n g i l A w o Lh g i Hw o Le d o M e v i e c e R h g i Hw o Lw o Le d o M t i m s n a r T Table 1. Mode Control Logic FILTER ALIGN MODE The ML2713 has three filters; the 2IF, discriminator, and data. Part of each filter is off chip, made up of external components, and part is on chip. The 2IF and discriminator filters have external inductors and capacitors configured to give a bandpass characteristic. In the Filter Align mode the ML2713 will adjust an on chip capacitor array that is in parallel with the external capacitance to correct for any tolerances in the external components values, thereby centering the bandpass filters to the correct frequency. In this way any production trimming of the filters is eliminated. The data filter is made up of on chip op-amps and off chip resistors and capacitors and does not need to be aligned or trimmed. The Filter Align mode can be disabled by tying MS1 to VCC4. In the Filter Align mode the ML2712 provides an 8MHz signal to the 2LO port, pins 2LO and 2LOB, of the ML2713. The 2LO port is a low impedance common base stage such that the 2LO signal is not attenuated by the parasitic capacitance of the ML2712, ML2713, the interconnect between them, and their packages. The 2LO port then drives the 2IF filter, and a frequency divider. The frequency divider divides the 8MHz signal down to a 500kHz which then clocks a 7-bit up/down counter. The 2IF filter will remove the fundamental of this signal, and pass the third harmonic at 24Mhz through a 0/90 degree phase splitter to the limiters which in turn drive the discriminator. The output of the discriminator connects to a low pass filter, which then drives a comparator. This comparator looks to see if the discriminator output is greater than or less than zero volts differential. If the discriminator filter bandpass characteristic is centered properly on 24MHz, then the 24MHz input to the discriminator should result in a zero signal at the discriminator output. If the center frequency is too high, the discriminator output will go high. If the center frequency is too low, the discriminator output will go low. A high or a low here will signal the up/down counter to increment or decrement respectively. The up/down counter then drives three identical variable capacitor arrays, leading to changes in on chip capacitors. Two of these on chip capacitors are in parallel with off chip capacitors in the 2IF filter, and one is in parallel with the off chip capacitor in the discriminator filter. These will cancel any tolerance associated with the off chip components such that the center frequencies of both filters are properly centered. The 7 bit up/down counter begins at mid code of 128 levels, so there will be a maximum of 64 counts in either direction. Since the up/ down counter is clocked at the 500kHz frequency, the filters will align within 128 msec. Therefore, in a WLAN system, the filters can be re-aligned every time the radio hops to a new frequency because it can do so in less time than it takes for the PLLs to settle. When switching from Filter Align mode, the up/down counter freezes, keeping the 7-bit result of the alignment fixed. Whenever the ML2713 is put in the Sleep mode, the up/down counter resets to the mid point. Therefore, if the Filter Align is being used, the filters must be realigned prior to receiving or transmitting. Active circuits in Filter Align Mode are shown in Figure 1. |
Nº de peça semelhante - ML2713CH |
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Descrição semelhante - ML2713CH |
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