HSP50214BVCZ datasheet(21/62 Pages) RENESAS

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HSP50214B

FN4450 Rev 4.00

Page 21 of 62

May 1, 2007

output section. Without gain control, a signal at -72dBFS =

20log10(2-12) at the input would have only 4-bits of

resolution at the output (12-bits less than the full scale



16-bits). The potential increase in the bit resolution due to

processing gain of the filters can be lost without the use of

the AGC.

Figure 23 shows the Block Diagram for the AGC Section.

The FIR filter data output is routed to the Resampling and

Halfband filters after passing through the AGC multipliers

and Shift Registers. The outputs of the Interpolating

Halfband filters are routed to the Cartesian to Polar

coordinate converter. The magnitude output of the

coordinate converter is routed through the AGC error

detector, the AGC error scaler and into the AGC loop filter.

This filtered error term is used to drive the AGC multiplier

and shifters, completing the AGC control loop.

The AGC Multiplier/Shifter portion of the AGC is identified in

Figure 23. The gain control from the AGC loop filter is

sampled when new data enters the Multiplier/Shifter. The

limit detector detects overflow in the shifter or the multiplier

and saturates the output of I and Q data paths

independently. The shifter has a gain from 0 to 90.31dB in

6.021dB steps, where 90.31dB = 20log10(2N), when N = 15.

The mantissa provides an additional 6dB of gain in

0.0338dB steps where 6.0204dB = 20log10[1+(X)2-15],

where X = 215-1. Thus, the AGC multiplier/shifter transfer

function is expressed as:

where N, the shifter exponent, has a range of 0<N<15 and X,

the mantissa, has a range of 0<X<(215-1).

Equation 14 can be expressed in dB,

The full AGC range of the Multiplier/Shifter is from 0 to

96.331dB (20log10[1+(215-1)2-15] + 20log10[215] = 96.331).

Figure 21 illustrates the transfer function of the AGC

multiplier versus mantissa control for N = 0. Figure 22

illustrates the complete AGC Multiplier/Shifter Transfer

function for all values of exponent and mantissa control.

The resolution of the mantissa was increased to 16-bits in

the A Version, to provide a theoretical AM modulation level

of -96dBc (depending on loop gain, settling mode and SNR).

This effectively eliminates AM spurious caused by the AGC

resolution.

For fixed gains, either set the upper and lower AGC limits to

the same value, or set the limits to minimum and maximum

gains and set the AGC loop gain to zero.

The Cartesian to Polar Coordinate converter accepts I and Q

data and generates magnitude and phase data. The

magnitude output is determined by the Equation 15:

where the magnitude limits are determined by the maximum

I and Q signal levels into the Cartesian to Polar converter.

Taking fractional 2’s complement representation, magnitude

ranges from 0 to 2.329, where the maximum output is

The AGC loop feedback path consists of an error detector, error

scaling, and an AGC loop filter. The error detector subtracts the

magnitude output of the coordinate converter from the

programmable AGC THRESHOLD value. The bit weighting of

(EQ. 14)

AGC Mult/Shift Gain

N 1X

2

–

,



(EQ. 14A)

(AGC Mult/Shift Gain)dB

20log10 2

N 1X

2

-15 





FIGURE 21. AGC MULTIPLIER LINEAR AND dB TRANSFER

FUNCTION

0 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240

AGC CONTROL MANTISSA VALUES (TIMES 256)

G (dB)

G (LINEAR)

FIGURE 22. AGC GAIN CONTROL TRANSFER FUNCTION

100

064

128

192

AGC CONTROL WORD (MANTISSA x 256)

N = 15

N = 14

N = 13

N = 12

N = 11

N = 10

N = 9

N = 8

N = 7

N = 6

N = 5

N = 4

N = 3

N = 2

N = 1

N = 0

(EQ. 15)

1.64676 I

1.64676

1.0



1.0



1.64676 1.414



2.329

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