Datasheet

AFE5808A

SLOS729B –OCTOBER 2011–REVISED APRIL 2012

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Table 4. VCA Register Map (continued)

ADDRESS ADDRESS Default

FUNCTION DESCRIPTION

(DEC) (HEX) Value

59[8] 0x3B[8] 0 CW_SUM_AMP_PDN 0: Power down;

1: Normal operation

Note: 59[8] is only effective in TGC test mode.

59[9] 0x3B[9] 0 PGA_TEST_MODE 0: Normal CW operation;

1: PGA outputs appear at CW outputs

AFE5808A VCA Register Description

LNA Input Impedances Configuration (Active Termination Programmability)

Different LNA input impedances can be configured through the register 52[4:0]. By enabling and disabling the

feedback resistors between LNA outputs and ACTx pins, LNA input impedance is adjustable accordingly. Table 5

describes the relationship between LNA gain and 52[4:0] settings. The input impedance settings are the same for

both TGC and CW paths.

The AFE5808A also has 4 preset active termination impedances as described in 52[7:6]. An internal decoder is

used to select appropriate resistors corresponding to different LNA gain.

Table 5. Register 52[4:0] Description

52[4:0]/0x34[4:0] FUNCTION

00000 No feedback resistor enabled

00001 Enables 450 Ω feedback resistor

00010 Enables 900 Ω feedback resistor

00100 Enables 1800 Ω feedback resistor

01000 Enables 3600 Ω feedback resistor

10000 Enables 4500 Ω feedback resistor

Table 6. Register 52[4:0] vs LNA Input Impedances

52[4:0]/0x34[4:0] 00000 00001 00010 00011 00100 00101 00110 00111

LNA:12dB High Z 150 Ω 300 Ω 100 Ω 600 Ω 120 Ω 200 Ω 86 Ω

LNA:18dB High Z 90 Ω 180 Ω 60 Ω 360 Ω 72 Ω 120 Ω 51 Ω

LNA:24dB High Z 50 Ω 100 Ω 33 Ω 200 Ω 40 Ω 66.67 Ω 29 Ω

52[4:0]/0x34[4:0] 01000 01001 01010 01011 01100 01101 01110 01111

LNA:12dB 1200 Ω 133 Ω 240 Ω 92 Ω 400 Ω 109 Ω 171 Ω 80 Ω

LNA:18dB 720 Ω 80 Ω 144 Ω 55 Ω 240 Ω 65 Ω 103 Ω 48 Ω

LNA:24dB 400 Ω 44 Ω 80 Ω 31 Ω 133 Ω 36 Ω 57 Ω 27 Ω

52[4:0]/0x34[4:0] 10000 10001 10010 10011 10100 10101 10110 10111

LNA:12dB 1500 Ω 136 Ω 250 Ω 94 Ω 429 Ω 111 Ω 176 Ω 81 Ω

LNA:18dB 900 Ω 82 Ω 150 Ω 56 Ω 257 Ω 67 Ω 106 Ω 49 Ω

LNA:24dB 500 Ω 45 Ω 83 Ω 31 Ω 143 Ω 37 Ω 59 Ω 27 Ω

52[4:0]/0x34[4:0] 11000 11001 11010 11011 11100 11101 11110 11111

LNA:12dB 667 Ω 122 Ω 207 Ω 87 Ω 316 Ω 102 Ω 154 Ω 76 Ω

LNA:18dB 400 Ω 73 Ω 124 Ω 52 Ω 189 Ω 61 Ω 92 Ω 46 Ω

LNA:24dB 222 Ω 41 Ω 69 Ω 29 Ω 105 Ω 34 Ω 51 Ω 25 Ω

Product Folder Links: AFE5808A