MT312C ZARLINK [Zarlink Semiconductor Inc], MT312C Datasheet - Page 53

• Manufacturer Part Number: MT312C
• Description: Satellite Channel Decoder
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

8.2 Automatic Gain Control Read Registers
8.2.1 Measured Signal Level at MT312 Input. Register 19 (R)
B7-0:
When AGC is controlling the signal level, there is a direct relationship between SIG LEVEL and AGC REF:
NOTE: the signal level is measured at the output of the ADC before any digital filtering takes place. Hence the
reading includes all noise and other signal channels passed by the SAW or baseband filter.
8.2.2 Measured AGC Feed Back Value. Registers 108 - 110 (R)
AGC[13:0]:
To avoid having too large a number, the following formula extracts a number less than 10000:
Tuner input signal level = AGC[13-6] * 4 + AGC[5-4] / 64.
ERR DB[9:0]: The ERR DB is the difference between the expected signal level defined by AGC REF and
The way H/M/L registers work within the QPSK block is as follows. When you read the H register the 24-bit
value is dumped into a shadow register. You don't have to read M and L after this. However, what you must
NOT do is to read M and L (or just L of a 24 or 16-bit register) without reading H. The safest solution is to read
H/M/L in that order.
SIG LEVEL
AGC H
AGC M
AGC L
NAME
NAME
SIG LEVEL[11:4]:
SIG LEVEL * 8 = AGC REF
These two registers provide a measurement of the AGC error feed back value by the MT312 to
the front end. Reading the bytes does NOT reset the value.This measurement can be used to
provide an indication of the signal level at the input to the tuner.
received signal level. This is in a non-linear logarithmic scale (hence the notation DB).
ADR
ADR
108
109
110
19
B7
B7
This register provides a measurement of the MT312 input signal level. It
contains the 8 MSBs. The remaining 4 LSBs are contained in SIG LEV L
register 107 together with the front end AGC lock status flag. In almost all
conditions, it should only be necessary to read the high byte to determine the
incoming signal level. If further accuracy is required, then the remaining bits of
the lower byte should be read and the 12 bits combined into one number.
AGC[5:0] - Front end AGC (low byte)
SIG LEVEL[11:4] - Signal level at MT312 input
B6
ERR DB[7:0] - Error difference (low byte)
B6
AGC[13:6] - Front end AGC (high byte)
B5
B5
B4
B4
Automatic Gain Control
B3
B3
B2
B2
ERR DB[9:8]
B1
B1
B0
B0
R
MT312
R
R
R
hex
Def
hex
00
Def
00
00
00
53