AD6636BBCZ(Rev0) データシートの表示（PDF） - Analog Devices
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AD6636BBCZ Datasheet PDF : 72 Pages
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THEORY OF OPERATION
ADC INPUT PORT
The AD6636 features four identical, independent high speed
ADC input ports named A, B, C, and D. These input ports have
the flexibility to allow independent inputs, diversity inputs, or
complex I/Q inputs. Any of the ADC input ports can be routed
to any of the six tuner channels; that is, any of the six AD6636
channels can receive input data from any of the input ports.
Time-multiplexed inputs on a single port are not supported in
the AD6636.
These four input ports can operate at up to 150 MSPS. Each
input port has its own clock (CLKA, CLKB, CLKC, and CLKD)
used for registering input data into the AD6636. To allow slow
input rates while providing fast processing clock rates, the
AD6636 contains an internal PLL clock multiplier that supplies
the internal signal processing clock. CLKA is used as an input to
the PLL clock multiplier. Additional programmability allows the
input data to be clocked into the part either on the rising edge
or the falling edge of the input clock.
In addition, the front end of the AD6636 contains circuitry that
enables high speed signal-level detection, gain control, and
quadrature I/Q correction. This is accomplished with a unique
high speed level-detection circuit that offers minimal latency
and maximum flexibility to control all four input signals
(typically ADC inputs) individually. The input ports also
provide input power-monitoring functions via various modes,
and magnitude and phase I/Q correction blocks. See the
Quadrature I/Q Correction Block section for details.
Each individual processing channel can receive input data from
any of the four input ports individually. This is controlled using
3-bit crossbar mux-select bit words in ADC input control
register. Each individual channel has a similar 3-bit selection. In
addition to the four input ports, an internal test signal (PN—
pseudorandom noise sequence) can also be selected. This
internal test signal is discussed in the User-Configurable Built-
In Self-Test (BIST) section.
Input Data Format
Each input port consists of a 16-bit mantissa and a 3-bit
exponent (16 + 3 floating-point input, or up to 16-bit fixed-
point input). When interfacing to standard fixed-point ADCs,
the exponent bit should either be connected to ground or be
programmed as outputs for gain control output. If connected to
a floating-point ADC (also called gain ranging ADC), the
exponent bits from the ADC can be connected to the input
exponent bits of the AD6636. The mantissa data format is twos
complement, and the exponent is unsigned binary.
AD6636
The 3-exponent bits are shared with the gain range control bits
in the hardware. When floating-point ADCs are not used, these
three pins on each ADC input port can be used as gain range
control output bits.
Input Timing
The data from each high speed input port is latched either on
the rising edge or the falling edge of the port’s individual CLKx
(where x stands for A, B, C, or D input ports). The ADC clock
invert bit in ADC clock control register selects the edge of the
clock (rising or falling) used to register input data into the
AD6636.
CLKx
tSI
tHI
INx [15:0]
EXPx [2:0]
DATA n
DATA n + 1
Figure 21. Input Data Timing Requirements
(Rising Edge of Clock, x = A, B, C, or D for Four Input Ports)
CLKx
tSI
tHI
INx [15:0]
EXPx [2:0]
DATA n
DATA n + 1
Figure 22. Input Data Timing Requirements
(Falling Edge of Clock, x = A, B, C, or D for Four Input Ports)
The clock signals (CLKA, CLKB, CLKC, and CLKD) can
operate at up to 150 MHz. In applications using high speed
ADCs, the ADC sample clock, data valid, or data ready strobe
are typically used to clock the AD6636.
Connection to Fixed-Point ADC
For fixed-point ADCs, the AD6636 exponent inputs, EXP[2:0],
are not typically used and should be tied low. Alternatively,
because these pins are shared with gain range control bits, if the
gain ranging block is used, these pins can be used as outputs of
the gain range control block. The ADC outputs are tied directly
to the AD6636 inputs, MSB-justified. Therefore, for fixed-point
ADCs, the exponents are typically static and no input scaling is
used in the AD6636. Figure 23 shows a typical interconnection.
Rev. 0 | Page 19 of 72
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