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sinara-hw / Stabilizer_Piezo_Driver

SImple piezo driver mezzanine for Stabilizer
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schematic review #5

Open gkasprow opened 3 years ago

gkasprow commented 3 years ago

@JakubKajzer

JakubKajzer commented 3 years ago

the amplifier gain depends on the source output impedance. did you take it into account?

Yes, I simulated an amplifier with various capacitance at output. At lower gain, this problem is more visible, but due to significant series resistance at the output, the max gain peak is about 3dB at about 300kHz

connecting outputs of two amplifiers is not a good idea.

Sorry for that, my mistake. It is a good idea, to make an optomos switch at outputs instead of switching inputs?

did you simulate the signal chain with offsets?

Yes, offset is amplified with the same gain as an input signal. In a discrete driver, the gain is 100x, so the offset can easily saturate the driver. Should I lower the gain?

why R21 is 47Ohm?

I don't know what capacitances will be driven, so I decided to choose 47Ohm. This value should be less when driving bigger capacitances and should be higher when driving smaller capacitances (according to a datasheet of ADHV4702-1).

it would be good to add some signalization of overtemperature. Are you sure that the connection between TMP and SD is a good idea?

A red led on the front panel will be enough? Connecting TMP and SD together, according to the datasheet, provides overtemperature protection.

the idea behind the latch-up circuit was to protect the amplifier before too high a voltage, not temperature.

I added overtemperature protection because there wasn't any for the discrete driver. Should I add overvoltage protection?

what is the role of IC10?

I added IC10 to negate LM75 outputs, so LM75 could work without changing its internal registers.

do you think the 5V rail has low noise and stability so can be injected to the OFFSET input

Now I see that I should add a pi filter to offsets supply.

will OPA197 work with output close to rails under the load?

OPA197 can provide about 2mA at the output with a 0.1V swing from the power supply.

gkasprow commented 3 years ago

the amplifier gain depends on the source output impedance. did you take it into account?

Yes, I simulated an amplifier with various capacitance at output. At lower gain, this problem is more visible, but due to significant series resistance at the output, the max gain peak is about 3dB at about 300kHz

I meant SOURCE impedance, not the impedance of the amplifier

connecting outputs of two amplifiers is not a good idea.

Sorry for that, my mistake. It is a good idea, to make an optomos switch at outputs instead of switching inputs?

you need to switch both. Just use DIP switches to choose which one is connected to input and output. Make sure both cannot be selected

did you simulate the signal chain with offsets?

Yes, offset is amplified with the same gain as an input signal. In a discrete driver, the gain is 100x, so the offset can easily saturate the driver. Should I lower the gain?

yes, use full DAC range

why R21 is 47Ohm?

I don't know what capacitances will be driven, so I decided to choose 47Ohm. This value should be less when driving bigger capacitances and should be higher when driving smaller capacitances (according to a datasheet of ADHV4702-1).

OK, make it big, 0805 or so

it would be good to add some signalization of overtemperature. Are you sure that the connection between TMP and SD is a good idea?

A red led on the front panel will be enough? Connecting TMP and SD together, according to the datasheet, provides overtemperature protection.

OK, use red LED.

the idea behind the latch-up circuit was to protect the amplifier before too high a voltage, not temperature.

I added overtemperature protection because there wasn't any for the discrete driver. Should I add overvoltage protection?

If there is a risk that the user can setup dangerous voltage for driver IC, add such protection.

what is the role of IC10?

I added IC10 to negate LM75 outputs, so LM75 could work without changing its internal registers.

since we don't need such circuit for temperature protection, skip it.

do you think the 5V rail has low noise and stability so can be injected to the OFFSET input

Now I see that I should add a pi filter to offsets supply.

please add low noise LDO

will OPA197 work with output close to rails under the load?

OPA197 can provide about 2mA at the output with a 0.1V swing from the power supply.

OK

JakubKajzer commented 3 years ago

the amplifier gain depends on the source output impedance. did you take it into account?

Yes, I simulated an amplifier with various capacitance at output. At lower gain, this problem is more visible, but due to significant series resistance at the output, the max gain peak is about 3dB at about 300kHz

I meant SOURCE impedance, not the impedance of the amplifier

I checked this at simulation and due to low input impedance, at input should be placed a voltage follower like in discrete amplifier. But I noticed that DAC voltage is ±10V and there is only a 5V symmetrical supply. ±5V voltage follower is used in discrete amplifier, but this reduces DAC resolution. Is changing the supply of voltage followers to +10V...-4.5V (after LDOs) will be good? Have I missed something?

If there is a risk that the user can setup dangerous voltage for driver IC, add such protection.

The upper MOSFET in the discrete driver can go only 200V Vds. It is possible to change this MOSFET to something that can withstand 250V, like for example FQB9P25TM, in order to keep all the output voltage range?

gkasprow commented 3 years ago

sure, you can increase the supply to +/-12V. It is already available from Stabilizer. Yes, change the MOSFET, but use one with similar specs as the low-side one.

JakubKajzer commented 3 years ago

I've uploaded updated schematics.

dtcallcock commented 3 years ago

@JakubKajzer Can you post a pdf please?

JakubKajzer commented 3 years ago

@dtcallcock Of course schematic.PDF

gkasprow commented 3 years ago

the offset is derived from P5V0 which is not stable. It will break the precision. Please use a good reference source. We need two offset adjustment circuits. Please add an HV capacitor discharge circuit that will immediately discharge them once P12V0 disappears The discrete amplifier overcurrent protection won't work. It forms a positive feedback circuit. Moreover, the bias current is rising with temperature, think about compensating it.