Hi, all
When I traced the tv_rx.py code, I found that in order to adjust the RF AGC/IF AGC
the AUX DAC inside the AD9862 must be used. But I had several questions about this.
1). the AUX DAC bit width: in the code segment below, there is a magic number 4096
(2e12), but the bit width of AUX DAC is only 8 bits width(2e8=256).What is the relationship
between the 8-bit and 4096?
2). the gain/voltage formula:
Are there two formula approximation from the tuner datasheet ?
3). TV RX daughterboard
In the schematics, it is necessary to have two signals: AUX_DAC_A, and io_rx_00
to control the IF AGC setting. What is the use of io_rx_00 signal?
# Gain setting
def _set_rfagc(self,gain):
assert gain <= 60 and gain >= 0
if gain == 60:
voltage = 4
else:
voltage = gain/60.0 * 2.25 + 1.25
dacword = int(4096*voltage/1.22/3.3) # 1.22 = opamp gain
assert dacword>=0 and dacword<4096
self.rfagc = dacword
self._u.write_aux_dac(self._which, 1, dacword)
def _set_ifagc(self,gain):
assert gain <= 35 and gain >= 0
if gain == 35:
voltage = 3.5
else:
voltage = gain/35.0 * 2.1 + 1.4
dacword = int(4096*voltage/1.22/3.3) # 1.22 = opamp gain
assert dacword>=0 and dacword<4096
self.rfagc = dacword
self._u.write_aux_dac(self._which, 0, dacword)
Owen Wu
ASMedia
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