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rf_channel: rework bias
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@jordens
jordens committed Oct 9, 2020
1 parent e94b97a commit 3821a64
Showing 1 changed file with 29 additions and 34 deletions.
63 changes: 29 additions & 34 deletions src/rf_channel.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -831,17 +831,15 @@ impl RfChannel {
/// # Returns
/// The most recent power supply measurements of the channel.
pub fn get_supply_measurements(&mut self) -> SupplyMeasurements {
// Read the cached (scanned) ADC measurements from the monitor.
let voltages = self.i2c_devices.power_monitor.get_voltages().unwrap();

// The P5V0 rail goes through a resistor divider of 15K -> 10K. This corresponds with a 2.5x
// reduction in measured voltage.
let voltages = self
.i2c_devices
.power_monitor.get_voltages().unwrap();

let v_p5v0mp = voltages[3] * 2.5;
let i_p28v0ch = voltages[0] * (100.0 / 0.100 / 4300.0);

// The P5V current is sensed across a 100mOhm resistor with 100 Ohm input resistance. The
// output resistance on the current sensor is 6.2K Ohm.
// The 28V current is sensed across a 100mOhm resistor with 100 Ohm input resistance. The
// output resistance on the current sensor is 4.3K Ohm.
//
// From the LT6106 (current monitor) datasheet:
// Vout = Vsns * Rout / Rin
Expand All @@ -850,22 +848,14 @@ impl RfChannel {
// Vsns = Isns * Rsns
// Rsns = 100m Ohm
// Rin = 100 Ohm
// Rout = 6.2K Ohm
// Rout = 4.3K Ohm
//
// Vout = Isns * Rsns * Rout / Rin
// Isns = (Vout * Rin) / Rsns / Rout
let i_p5v0ch = voltages[1] * (100.0 / 0.100 / 6200.0);

SupplyMeasurements {
v_p5v0mp,
i_p28v0ch,
i_p5v0ch,
}
}
let i_p28v0ch = voltages[0] * (100.0 / 0.100 / 4300.0);

fn get_p28v_current(&mut self) -> f32 {
// The 28V current is sensed across a 100mOhm resistor with 100 Ohm input resistance. The
// output resistance on the current sensor is 4.3K Ohm.
// The P5V current is sensed across a 100mOhm resistor with 100 Ohm input resistance. The
// output resistance on the current sensor is 6.2K Ohm.
//
// From the LT6106 (current monitor) datasheet:
// Vout = Vsns * Rout / Rin
Expand All @@ -874,12 +864,21 @@ impl RfChannel {
// Vsns = Isns * Rsns
// Rsns = 100m Ohm
// Rin = 100 Ohm
// Rout = 4.3K Ohm
// Rout = 6.2K Ohm
//
// Vout = Isns * Rsns * Rout / Rin
// Isns = (Vout * Rin) / Rsns / Rout
let i_p5v0ch = voltages[1] * (100.0 / 0.100 / 6200.0);

SupplyMeasurements {
v_p5v0mp,
i_p28v0ch,
i_p5v0ch,
}
}

// Read the cached (scanned) ADC measurement from the monitor.
fn get_p28v_current(&mut self, delay: &mut impl DelayUs<u16>) -> f32 {
delay.delay_us(1000);
let p28v_rail_current_sense = self
.i2c_devices
.power_monitor
Expand All @@ -906,12 +905,12 @@ impl RfChannel {
///
/// # Returns
/// The reflected power in dBm.
pub fn get_reflected_power(&mut self, mut adc: &mut hal::adc::Adc<hal::stm32::ADC3>) -> f32 {
pub fn get_reflected_power(&mut self, adc: &mut hal::adc::Adc<hal::stm32::ADC3>) -> f32 {
let sample = self
.pins
.adc_pins
.reflected_power
.convert(&mut adc, SampleTime::Cycles_480);
.convert(adc, SampleTime::Cycles_480);
let voltage = adc.sample_to_millivolts(sample) as f32 / 1000.0;

self.settings.data.reflected_power_transform.map(voltage)
Expand All @@ -924,12 +923,12 @@ impl RfChannel {
///
/// # Returns
/// The output power in dBm.
pub fn get_output_power(&mut self, mut adc: &mut hal::adc::Adc<hal::stm32::ADC3>) -> f32 {
pub fn get_output_power(&mut self, adc: &mut hal::adc::Adc<hal::stm32::ADC3>) -> f32 {
let sample = self
.pins
.adc_pins
.tx_power
.convert(&mut adc, SampleTime::Cycles_480);
.convert(adc, SampleTime::Cycles_480);
let voltage = adc.sample_to_millivolts(sample) as f32 / 1000.0;

self.settings.data.output_power_transform.map(voltage)
Expand Down Expand Up @@ -995,9 +994,7 @@ impl RfChannel {
// Place the RF channel into pinch-off to start.
let mut bias_voltage = -3.2;
self.set_bias(bias_voltage).unwrap();
// Settle the bias
delay.delay_us(12000);
let mut last_current = self.get_p28v_current();
let mut last_current = self.get_p28v_current(delay);

// First, increase the bias voltage until we overshoot the desired set current by a small
// margin.
Expand All @@ -1010,10 +1007,9 @@ impl RfChannel {
}

self.set_bias(bias_voltage).unwrap();
delay.delay_us(12000);

// Re-measure the drain current.
let new_current = self.get_p28v_current();
let new_current = self.get_p28v_current(delay);

// Check that the LDO did not enter fold-back. When the LDO enters fold-back, the
// current should begin to drop dramatically. For now, a 20mA threshold is used to
Expand All @@ -1024,20 +1020,19 @@ impl RfChannel {
last_current = new_current;
}

let high_voltage = bias_voltage;
// let high_voltage = bias_voltage;

// Next, decrease the bias voltage until we drop back below the desired set point.
while last_current > desired_current {
// Decrease the bias voltage in 1mV steps to decrease the drain current marginally.
bias_voltage = bias_voltage - 0.001;
if bias_voltage <= -3.2 || bias_voltage < high_voltage - 0.040 {
if bias_voltage <= -3.2 { // || bias_voltage < high_voltage - 0.040 {
return Err(Error::Invalid);
}

// Set the new bias and re-measure the drain current.
self.set_bias(bias_voltage).unwrap();
delay.delay_us(12000);
last_current = self.get_p28v_current();
last_current = self.get_p28v_current(delay);
}

// Note that we're returning the actual bias voltage as calculated by the DAC as opposed to
Expand Down

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