HSP50215 데이터 시트보기 (PDF) - Intersil

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HSP50215

Digital UpConverter

Intersil 

HSP50215

Data enters the FIFO with a write command to either Control

Word 0 (for I data), or Control Word 1 (for Q data). This

transfers data from the microprocessor holding register into the

first 16-bit register of the FIFO. The FIFO counter is

incremented every time data is written into the FIFO. Four

REFCLK periods are required from the rising edge of a WR

signal before another WR rising edge can occur, (i.e., before

data can once again be written into either the I or Q FIFO). This

limits the maximum data input (write) rate to 52MHz/4 =

13MHz.

NOTE: The Write rate is not the parameter that determines the

maximum input rate, the shaping filter is. The maximum in-

put for the shaping filter is 52MHz/(IP)(DS), which is

52MHz/16 = 3.25 MHz for a minimal shaping filter (DS = IP =

4). See the Shaping Filter Section for more details.

The timing details of these FIFO registers are shown in Figure

2. While the data for the I and Q inputs are independent, the

Write cycle limitations of the FIFO constrains the maximum

input symbol rate of quadrature symbols (both I and Q data) as

noted.

When the Shaping Filter requires another sample of data, a

request is made to the FIFO for data and the FIFO counter is

decremented. Figure 3 indicates the timing of a request for data

from the Shaping filter to the actual appearance of data at the

FIFO output. The FIFO has circuitry for detecting an empty

FIFO as well as a full FIFO. An “empty” FIFO detection causes

“zero” data to be entered into the shaping filter. A “full” FIFO

detection prevents data from being pushed out of the FIFO

before the filter requests it.

NOTE: Do not write to a full FIFO. Writing to a full FIFO is an er-

ror condition and the part will be reset to prevent trans-

mission of erroneous data over the air.

A programmable FIFO depth threshold sets when the

FIFORDY signal is asserted, alerting the data source that more

data is required. The FIFORDY signal assists a data source in

maintaining the desired FIFO data depth. Control Word 18, bits

0-2 are used to set the data FIFO depth threshold for both I and

Q inputs.

NOTE: SAMPCLK may be used instead of FIFORDY to indicate

that data is transferred from the FIFO to the shaping filter.

See the Pin Description Table.

.

REFCLK

EnFIFO

IFIFO

FIGURE 3. FIFO DATA AND ENABLE TIMING

Data Modulation Path

Three data path options are provided, one for each

modulation format. The modulation format is selected using

Control Word 16 (See the Microprocessor Write section).

Control Word 16 bits (1:0) are defined as: 00:QASK, 01:FM

with post-modulation filtering, and 10:FM with pre-

modulation pulse shaping. These modulation paths are

defined in the following subsections.

Modulation Mode 00 - QASK

This modulation mode configures the PUC as a BPSK,

QPSK, OQPSK, MSK or m-QAM modulator. The filter

configuration is shown in Figure 4. The data FIFO outputs

are routed to the shaping filters. Here the samples are

interpolated by 4, 8, or 16 and shaped using a FIR filter with

up to a 256 taps. The filter impulse response can span 4-16

input samples. A half (input) sample delay can be set in the I

channel for implementing OQPSK modulation. The output of

the shaping filter is routed through a gain adjust multiplier

and into the interpolation filter. The interpolation filter

interpolates by a factor set in the resampling NCO. The

output of the interpolation filter is at the master clock

frequency, REFCLK. The samples are then mixed with the

carrier L.O. for quadrature upconversion. The output is then

summed with the cascade input signal, saturated (in the

case of overflow), and formatted for output.

I

SHAPING

INTERPOLATION

TO

Q

FILTER

FILTER

MODULATOR

FIGURE 4. QASK

Modulation Mode 01 - FM with BANDLIMITING

Filter

This mode configures the PUC as an FM modulator with

post-modulation filtering. This mode provides for FSK and

FM modulation schemes. In this mode, the I input samples

drive the frequency control section of a quadrature NCO to

produce a zero IF FM signal. The FM quadrature signals are

then routed to the shaping FIR filter and into the interpolation

filter for bandlimiting and interpolation up to the master clock

rate as shown in Figure 5. The quadrature filtered FM signals

are then upconverted to the carrier frequency by the carrier

NCO and mixers. The output is then summed with the

cascade input signal, saturated (in the case of overflow), and

formatted for output. Note that pulse shaping in this mode

must be provided prior to the PUC.

FM

I

MODULATOR

SHAPING

FILTER

INTERPOLATION

FILTER

FIGURE 5. FM WITH BANDLIMITING

Modulation Mode 10 - FM with Pulse Shaping

This mode configures the PUC as an FM modulator with pre-

modulation baseband pulse shaping. The data from the

FIFO (I channel only) is routed to the FIR shaping filter. The

FIR shaping filter output drives the frequency control section

3-427

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