HSP50214A 데이터 시트보기 (PDF) - Intersil

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HSP50214A

Programmable Downconverter

Intersil 

HSP50214A

a gain error for use in an AGC loop with either the RF/IF or

A/D converter stages (see Figure 8). The AGC loop

includes Input Level Detector, the microprocessor and an

external gain control amplifier (or attenuator). The input

samples are rectified and added to a threshold pro-

grammed via the microprocessor interface, as shown in

Figure 9. The bit weighting of the data path through the

input threshold detector is shown in Figure 10. The thresh-

old is a signed number, so it should be set to the inverse of

the desired input level. The threshold can be set to zero if

the average input level is desired instead of the error. The

sum of the threshold and the absolute value of the input is

accumulated in a 32-bit accumulator. The accumulator can

handle up to 218 samples without overflow. The integration

time is controlled by an 18-bit counter. The integration

counter preload (ICPrel) is programmed via the micropro-

cessor interface through Control Word 1. Only the upper 16

bits are programmable. The 2 LSBs are always zero. Con-

trol Word 1, Bits 29-14 are programmed to:

ICPrel = (N) ⁄ 4 + 1

(EQ. 1)

where N is the desired integration period, defined as the

number of input samples to be integrated. N must be a multi-

ple of 4: [0, 4, 8, 12, 16 .... , 218].

INPUT LEVEL DETECTOR †

STATUS (0) †

LEVEL

DETECT

INPUT_THRESH †

INTG_MODE †

INTG_INTEVAL †

14

IN(13:0)

INPUT

FORMAT †

GAINADJ(2:0)

14

18

18

NCO † †

4

EN

DELAY 3

LIMIT

3

∑

ENI

INTERP †

CONTROL WORD 0

CONTROL WORD 1

CLKIN

CONTROL

LOGIC

4

DELAY 3

INPUT_MODE †

INPUT_FMT †

INPUT_THRESH †

INTG_MODE †

INTG_INTEVAL †

BYPASS †

† Controlled via microprocessor interface.

†† See NCO Section for more details.

FIGURE 3. BLOCK DIAGRAM OF THE INPUT SECTION

BYPASS

5MHz

CIC

FILTER

MIN. R = 4

PROCCLK = 28MHz

HB/FIR FILTER

MAX. fS = 4MHz

(EXCEEDED IN

BYPASS PATH)

500kHz = 85dB

BANDWIDTH

(NOT ACHIEVED

WITH CIC FILTER

PATH)

↑8 (0 STUFF) = 40MHz

4MHz

5MHz

CIC FILTER

R = ↓10

HB/FIR FILTER

500kHz = 85dB

BANDWIDTH

Without Interpolation, the CIC bypass path exceeds the HB/FIR filter

input sample rate and the CIC filter path will not yield the desired 85dB

dynamic range band width of 500kHz.

FIGURE 4. STATEMENT OF THE PROBLEM

FIGURE 5. BLOCK DIAGRAM OF THE INTERPOLATION

APPROACH

9

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