HMC1010　Log slope and intercept calculation formulas

Hi,

My customers are considering HMC 1010.

I got a question about calculation formula of log slope and interception.

If we use RFBK = 4.7 KΩ, RSHUNT = 2.2 KΩ, and RSET = 24 KΩ when determining β on page 11-22, the calculation result is β = 3.33.
However, it is β = 1.67 in the data sheet.

Where did 1/2 come from?

The HMC 1020 data sheet has the same circuit diagram.
However, the formula for determining β = 1/2 (RFBK / (RFBK // RSHUNT // RSET)))).
Is the formula in HMC 1010 data sheet wrong?

Best regards,

Yuya

Parents
• Hello Yuya,

Standard demo board uses RFBK= RSHUNT= 4.7k. This means output amp Gain= 2. In this standard configuration, slope= 37.3 mV/dB.

Changing RSHUNT= 2.2k and RSET= 24k will increase the slope. Now output amp Gain= 3.3322.

When reconfiguring the demo board for more or less output amplifier gain (or slope), Beta is the ratio of gain increase or decrease. In this example, Beta= 3.3322/2= 1.666. This means Optimized slope= 1.666 * 37.3 = 62 mV/dB, as stated in datasheet.

The generalized formula for Beta is:   Beta= ((RSHUNT || RSET) + RFBK) / 2 (RSHUNT || RSET). The factor of 2 comes from Beta being a relative term (the unmodified demo board output amplifier Gain = 2). It seems that both datasheets have the wrong formula for Beta.

Hope that helps.