What kind of spec is good and reasonable for Mixer?

[yolande_yj]

The mixer design contains a lot of balances. I know the spec is largely depend on the application, but there should be some commonsense there. For example, when designing LNA, we say a -10db S11 should be garentee, a NF less than 2 is good, the gain is more or less around 20dB (narrow band) and a reverse isolation of about -30 db is acceptable ....

For downconversion mixer (frequency from 1.6G to 10MHz), can you add your comment like this? Or what do you think the spec inside the bracket?

Application: (Low IF receiver)
Process: (SiGe)
Structure: (Single Balance active)
Power: (1.8V x 2mA)
Conversion Gain: (2 db)
P1dB: (-10 dbm)
IIP3: (3 dbm)
NF: (8 db)
Output load: (1k ohm)
LO to IF isolation: (-30 db)

 

[yibinhsieh]

Application: (Low IF receiver)
Process: (SiGe)
Structure: (Single Balance active)
Power: (1.8V x 2mA)
Conversion Gain: (2 db)
P1dB: (-10 dbm)
IIP3: (3 dbm)
NF: (8 db)
Output load: (1k ohm)
LO to IF isolation: (-30 db)

Conversion gain is too small. Usually 10db is reasonable.
P1dB and IIP3 is good.
NF is too good. NF is usually is larger than 10dB.
LO to IF isolation: I don't think you can reach this value in Single Balance.

Yibin.

 

[yolande_yj]

Conversion gain is too small. Usually 10db is reasonable.
P1dB and IIP3 is good.
NF is too good. NF is usually is larger than 10dB.
LO to IF isolation: I don't think you can reach this value in Single Balance.

Yibin.

Thank you. But I have questions:
1. For a low power design, do you think 10db conversion gain is achievable? If use passive mixer, we can only get conversion loss. Why do you need a high gain like this?
2. I think the most important spec for mixer is the linearity. As you say the P1dB and IIP3 are good, so you must have a number in mind, above which you will consider it good. Can you tell me the number? And why is that number?
3. NF should be larger and LO2IF iso could be smaller --- I agree. Normally how much iso can we get for single balance mixer?

 

[jupitorcuu]

IIP3 is only 3dBm is too small. Also outputload is 1Kohm. it looks strenge with single end.
It is according to system requirement. If you want to use it on very high linearity receiver, it should be problem.