GC5316 datasheet(8/75 Pages) TI

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GC5316

SLWS154A − JANUARY 2004 − REVISED MARCH 2004

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2.3

Receive Downconverter Function Blocks

AGC

CFIR Filter

D ecby2

F requency

Phase

NC O

Delay Adjust

I,Q

Serial

Interface

up to 18 bits

(25bitswith

AGC disabled)

PFIR Filter

D ecby1

Six Stage

CI C Filter

D ec4− 32

4to 2

Select

Zero Pad

serial

RM S Power

M easure

Figure 6. Receive Downconverter Function Blocks

The GC5316 downconversion channel can process two CDMA carriers or a single UMTS carrier. Signal data is

selected from one of four ports and can be either real or complex. Data from the selected port is multiplied with a

complex, programmable numerically controlled oscillator (NCO) which tunes the signal of interest to baseband. The

delay adjust and zero pad blocks permits adjustment of the delay in the end-to-end channel. Zero padding

interpolates the signal to the rxclk rate. Filtering consists of a six stage CIC filter which decimates the tuned data by

a factor from 4 to 32, a compensating FIR filter (CFIR) which decimates by a factor of two, followed by a

programmable FIR filter (PFIR) which does not decimate.

The RMS power meter measures the power within the channel’s bandwidth. The AGC automatically drives the gain

and keeps the magnitude of the signal at a user-specified level. This allows fewer bits to represent the signal. The

serial output interface formats and rounds the output data. Each of the above blocks is described in greater detail

in the following sections.

2.3.1 Receive Mixer

Sin

Cos

From Input

D ata Interface

To Channel Delay

From N CO

De−Mux

& Round

Input

Select

Figure 7. Receiver Mixer

The input select routes one of the four buses in rx_distribution to the I port and a second bus to the Q port of the mixer.

In CDMA mode, bus selection is time multiplexed so the two channels may select different data sources if desired.

Table 6 shows the bus selection.

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