GC3021 datasheet(18/37 Pages) TI1

18 / 37 page

GRAYCHIP, INC.

- 16 -

JUNE 22, 1998

GC3021 MIXER AND CARRIER REMOVAL CHIP

DATA SHEET

This document contains information which may be changed at any time without notice

4.1

MODE CONTROL REGISTER

This register contains the mode control bits. The suggested default value is 5280 (HEX).

ADDRESS 0:

MODE_REG

BIT

TYPE

NAME

DESCRIPTION

0,1 (LSBs)

R/W

INPUT[0:1]

This two bit field controls the input data selection. The

input modes are:

INPUT

DESCRIPTION

Complex data input

High speed real data input

Diagnostic ramp input

Zero input

R/W

REC_ENABLE

Turns on the differential receivers. The high speed input

data and clock signals are cleared when this bit is low.

R/W

PTERM_ENABLE

Turns on the termination resistors to VTERM for the

positive rail (I) data and HSI inputs.

R/W

NTERM_ENABLE

Turns on the termination resistors to VTERM for the

negative rail (Q) data and HSI inputs.

R/W

PCK_ENABLE

Turns on the termination resistor to VTERM for HCK.

R/W

NCK_ENABLE

Turns on the termination resistor to VTERM for HCK.

R/W

MIXER_ROUND

Round the mixer multiplier products to 12 bits. The

products are truncated to 12 bits if this control is low.

R/W

ADDER_CLEAR

Clears one input to the adder in the mixer circuit to allow

the Ieven and Qeven outputs to be routed to the symbol

offset circuitry. See Section 2.5.

R/W

2X_GAIN

Enables the 2X gain circuit in the mixer circuit.

R/W

OFFSET

Delays the I sample in the symbol offset circuit by one

clock cycle relative to the Q sample.

R/W

OFFSET_HOLD

Samples and holds every other I,Q pair in the symbol

offset circuit. The OFFSET_SYNC mode (See Section

4.2) determines how the sample and hold timing is

synchronized to the input data.

R/W

QMAP_ENABLE

Enables the quadrant map mode. This mode maps the

I,Q pairs into the first quadrant for phase error lookup

when this mode is selected. The error is then mapped

back to the correct quadrant after it is looked up in the

phase error memory.

R/W

QMAP_ROUND

Round instead of truncate the I,Q samples in the phase

error circuit. If QMAP_ENABLE is set the values are

rounded into the 7 MSBs, otherwise they are rounded to

the 6 MSB.

R/W

QMAP_INVERT

Convert negative numbers to positive numbers in the

Qmap mode by inverting the data bits (1’s complement

negation) rather than negating them.

R/W

NCO_MODE

Turns on the high speed NCO mode. Must be high for

the high speed double rate input mode, low otherwise.

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