comments for DVB LNA API
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Hi Antti,
Quoted 15 lines · Antti Palosaari
I am looking how to implement LNA support for the DVB API.
What we need to be configurable at least is: OFF, ON, AUTO.
There is LNAs that support variable gain and likely those will be sooner or later. Actually I think there is already LNAs integrated to the RF-tuner that offers adjustable gain. Also looking to NXP catalog and you will see there is digital TV LNAs with adjustable gain.
Coming from that requirements are:
adjustable gain 0-xxx dB
LNA OFF
LNA ON
LNA AUTO
Quoted 3 lines
Setting LNA is easy but how to query capabilities of supported LNA values? eg. this device has LNA which supports Gain=5dB, Gain=8dB, LNA auto?
Without having a sample of device capabilities this question may be irrelevant, but what if the gain is somewhat continuiously configurable vs. discretized? For example can some be configured just for 5,8 and 11, whilst some might have some 8-bit value that controls gain between 5 and 11?
Quoted 3 lines
LNA ON (bypass) could be replaced with Gain=0 and LNA ON with Gain>0, Gain=-1 is for auto example.
How should the API handle differences between the specified gain and the capabilities of the LNA? Round to nearest possible config if it's within the operating range; return error if out of range?
Quoted 6 lines
regards
Antti
Signature · 2 lines
Steve Kerrison MEng Hons. http://www.stevekerrison.com/
Quoted 16 lines · Steve Kerrison
Quoted 15 lines · Antti Palosaari
I am looking how to implement LNA support for the DVB API.
What we need to be configurable at least is: OFF, ON, AUTO.
There is LNAs that support variable gain and likely those will be sooner or later. Actually I think there is already LNAs integrated to the RF-tuner that offers adjustable gain. Also looking to NXP catalog and you will see there is digital TV LNAs with adjustable gain.
Coming from that requirements are:
adjustable gain 0-xxx dB
LNA OFF
LNA ON
LNA AUTO
Quoted 8 lines
Quoted 3 lines
Setting LNA is easy but how to query capabilities of supported LNA values? eg. this device has LNA which supports Gain=5dB, Gain=8dB, LNA auto?
Without having a sample of device capabilities this question may be irrelevant, but what if the gain is somewhat continuiously configurable vs. discretized? For example can some be configured just for 5,8 and 11, whilst some might have some 8-bit value that controls gain between 5 and 11?
Yes.
For example external DVB-T/C LNA NXP BGU7033. It does have 3 modes, 10 dB, 5 dB and bypass -2 dB.
LNAs offering more adjustable gain is called VGA (variable gain amplifier). It could have control interface like 5-bits or some other bus like I2C. Those are usually integrated to the silicon RF-tuner and in that case configuration is possible via tuner registers. Usually it is not needed to configure at all on run-time.
Quoted 6 lines
Quoted 2 lines
LNA ON (bypass) could be replaced with Gain=0 and LNA ON with Gain>0, Gain=-1 is for auto example.
How should the API handle differences between the specified gain and the capabilities of the LNA? Round to nearest possible config if it's within the operating range; return error if out of range?
I think rounding is best approach.
Maybe it is not necessary to read at all. Just allow user set LNA in steps of one number, 0, 1, 2, 3, ..., 100 and let the driver detect scale. In that case simple LNA having only one static gain value has values: AUTO, 0, 1. LNA having 2 gain levels: AUTO, 0, 1, 2. VGA having 3 bit control: AUTO, 0, 1, 2, 3, 4, 5, 6, 7.
regards
Antti
Signature · 1 line
http://palosaari.fi/