
4-10
RSSI A/D Interface
The Receive Signal Strength Indication (RSSI) analog signal is
input to a 6-bit A/D, indicating 64 discrete levels of received
signal strength. This A/D measures a DC voltage, so its input
must be DC coupled. Pin 16 (V
REFP
) sets the reference for the
RSSI A/D converter. V
REFP
is common for the I and Q and
RSSI A/Ds. The RSSI signal is used as an input to the Clear
Channel Assessment (CCA) algorithm of the HFA3860. The
RSSI A/D output is stored in an 6-bit register available via the
TEST Bus and the TEST Bus monitor register. CCA is further
described on page 15.
The interface specifications for the RSSI A/D are listed in
Table 4 below (V
REFP
= 1.75V).
Test Port
The HFA3860 provides the capability to access a number of
internal signals and/or data through the Test port, pins TEST
7:0. In addition pin 1 (TEST_CK) is an output that can be
used in conjunction with the data coming from the test port
outputs. The test port is programmable through configuration
register (CR28). Any signal on the test port can also be read
from configuration register (CR29) via the serial control port.
There are 32 modes assigned to the PRISM test port. Some
are only applicable to factory test (Table 5).
D/A
D/A
SELECT
+FS OR -FS
COMPARE
+FS OR -FS
COMPARE
ACCUMULATOR
(25-BIT)
TEST REG
MODE 1 (7)
REG
A/DCAL
TEST REG
MODE 25 (8:0)
A/D_CAL_ACCUM
(1/4 dB PER LSB)
A/D_CAL_CK
(APPROX 1KHz)
A/D
A/D
RX_I_IN
RX_Q_IN
A/D_CK
/3
/3
A/D_CAL_POS
A/D_CAL_NEG
/8
/8
TO RSSI A/D
V
REFN
V
REFP
ANALOG
BIASES
8
5 MSBs
5
TO CORRELATOR
FIGURE 7. A/D CAL CIRCUIT
TABLE 4. RSSI A/D SPECIFICATIONS
PARAMETER
MIN
TYP
MAX
Full Scale Input Voltage
-
-
1.15
Input Bandwidth (0.5dB)
1MHz
-
-
Input Capacitance
-
7pF
-
Input Impedance (DC)
1M
-
-
TABLE 5. TEST MODES
MODE
DESCRIPTION
TEST_CLK
TEST (7:0)
0
Quiet Test Bus
0
00
1
RX Acquisition
Monitor
Initial Detect
A/DCal, CRS, ED,
Track, SFD Detect,
Signal Field Ready,
Length Field Ready,
Header CRC Valid
2
TX Field Monitor
IQMARK
A/DCal,TXPEInternal,
Preamble Start, SFD
Start, Signal Field
Start, Length Field
Start, CRC Start,
MPDU Start
3
RSSI Monitor
RSSI Pulse
CSE Latched, CSE,
RSSI Out (5:0)
4
SQ1 Monitor
Pulse after
SQ is valid
SQ1 (7:0)
5
SQ2 Monitor
Pulse after
SQ is valid
SQ2 (7:0)
6
Correlator Lo
Rate
Sample CLK
Correlator Magnitude
(7:0)
7
Freq Test Lo
Rate
Subsample
CLK
Frequency Register
(18:11)
8
Phase Test Lo
Rate
Subsample
CLK
Phase Register (7:0)
9
NCO Test Lo
Rate
Subsample
CLK
NCO Register (15:8)
HFA3860