Closed-Loop RF Gain Control

The MAX2163 can provide either open-loop RF gain

control by the GC1 pin or closed-loop RF automatic

gain control (AGC) by the on-chip power detector.

Automatic RF gain control is enabled by setting the

PDBM[1:0] bits to 00 as shown in the PDET/RF-FILT

register (Table 6). Setting the PDBM[1:0] bits to 10

allows open-loop RF gain control by the GC1 pin.

When the RF AGC loop is disabled, RF gain is con-

trolled by an external voltage that is applied to the GC1

pin. The GC1 pin’s input voltage range is 0.3V to 2.1V

with 0.3V providing the maximum RF gain.

When the RF AGC loop is enabled, the IF power detec-

tor output is internally connected to the GC1 input and

the RF gain is controlled by the power detector’s output

voltage. An external capacitor connected from the GC1

pin to ground sets the AGC loop response time. The

loop response time is calculated as follows:

where:

R = 1k

Ω

farads.

The attack point (referred to as the RF input) of the AGC

loop can be programmed from -66dBm to -52dBm and

is controlled by the PDET[2:0] bits in the PDET/RF-FILT

register (Table 6).

High-Side and Low-Side LO Injection

The MAX2163 allows selection between high-side and

low-side LO injection through the HSLS bit in the MODE

register (Table 7). To select low-side injection, set HSLS

to 1; to select high-side injection, set HSLS to 0.

IF Filter

The nominal IF filter center frequency and bandwidth

are 571kHz and 860kHz, respectively.

The center frequency of the IF bandpass filter is tuned

at the factory; however, the factory-set trim can be

bypassed and the center frequency can be adjusted

through the FLTS and TUN[2:0] bits in the IF Filter reg-

ister (Table 3). Set the FLTS bit to 0 to select the filter’s

center frequency to the factory-set tuning. Set the FLTS

bit to 1 to allow the filter’s center frequency to be

adjusted with the TUN[2:0] bits (Table 3).

VCO Autoselect (VAS)

The MAX2163 includes three VCOs with each VCO hav-

ing 16 sub-bands. The appropriate VCO and VCO sub-

band for the desired local oscillator frequency can be

manually selected by programming the VCO[1:0] and

VSB[3:0] bits in the VCO register. The selected VCO and

sub-band is reported in the VAS STATUS register (read

only) (Table 13).

Alternatively, the MAX2163 can be set to autonomously

choose a VCO and VCO sub-band. Automatic VCO

selection is enabled by setting the VAS bit in the VAS

register (Table 4) and is initiated once the N-divider LSB

register word is loaded. In the event that the R-divider

is changed, both the R-Divider MSB and R-Divider

LSB registers must be reprogrammed. Also, if the

R-Divider or the N-Divider MSB is changed, the

N-Divider LSB register must also be reprogrammed to

initiate the VCO autoselect function. The VCO and

VCO sub-band that are programmed in the VCO[1:0] and

VSB[3:0] bits serve as the starting point for the automatic

VCO selection process when VASS = 0. When VASS = 1,

the current VCO and VCO sub-bands serve as the start-

ing point for the automatic VCO selection process.

During the selection process, the VASE bit in the VAS

STATUS register is cleared to indicate the autoselection

function is active. Upon successful completion, bits VASE

and VASA are set and the VCO and sub-band selected

are reported in the VAS STATUS register (Table 13). If the

search is unsuccessful, VASA is cleared and VASE is set.

This indicates that searching has ended, but no VCO has

been found, and occurs when trying to tune to a frequen-

cy outside the VCO’s specified frequency range.

Charge-Pump Select (CPS)

The MAX2163 allows for manual selection of the

charge-pump current (CPS = 0) or automatic selection

(CPS = 1). When in manual mode, the charge-pump

current is programmed by bits CP[1:0] in the R-Divider

LSB register (Table 9). In automatic selection mode, the

charge-pump current is automatically set based on

VTUNE voltage and current VCO sub-band. ADE, ADL,

and VAS bits must be programmed to 1. The selected

charge-pump current is reported in Table 18 .

ISDB-T 1-Segment Tuner

20

______________________________________________________________________________________

VSB[3]

ADC[2]

CP (mA)

0

0

2

0

1

3

1

0

1.5

1

1

2.5

Table 18. Charge-Pump Current Setting

When CPS = 1