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Data Sheet

HMC1126ACEZ

Rev. 0 | Page 19 of 21

CONSTANT DRAIN CURRENT BIASING vs.

CONSTANT GATE VOLTAGE BIASING

Voltage Biasing

The HMC920LP5E uses closed loop feedback to continuously

adjust VGATE to maintain a constant drain current bias over the

dc supply variation, temperature, and part to part variations.

Constant drain current bias is an ideal method for reducing

time in calibration procedures and maintaining consistent

performance over time.

In comparison to a constant gate voltage bias, where the current

increases dynamically when the RF power is applied, a constant

drain current bias results in constant power consumption.

The OP1dB performance for the constant drain current bias

can be varied by varying the bias setpoint. By increasing the bias

current, OP1dB increases, as shown in Figure 66. The trade-off

with a constant drain current is that this higher drain current is

present for all RF input and output power levels.

The current and temperature limit of IDD under the constant

current operation is usually set by the thermal limitations

detailed in the Absolute Maximum Ratings section (see the

continuous power dissipation specification in Table 5).

Increasing IDD does not indefinitely increase OP1dB. Therefore,

consider the trade-off between the power dissipation and OP1dB

performance when using a constant drain current bias.

The performance of the constant drain current circuit is

summarized in Figure 60 to Figure 67. These figures include

comparisons with a constant gate voltage bias. Note that Figure 60

indicates a current consumption of 140 mA, which includes the

complete current consumption of the circuit, that is, 120 mA drain

current for the HMC1126ACEZ and an additional 20 mA of

quiescent current in the HMC920LP5E. Using 140 mA as the

current consumption also results in lower PAE compared to a

constant gate voltage bias.

180

110

160

140

120

100

130

170

150

–10

–5

INPUT POWER (dBm)

CONSTANT DRAIN CURRENT BIAS

CONSTANT GATE VOLTAGE BIAS

Figure 60. IDD vs. Input Power, VDD = 5 V, Frequency = 26 GHz, Constant Drain

Current Bias (IDD = 140 mA) and Constant Gate Voltage Bias

–10

–5

INPUT POWER (dBm)

CONSTANT DRAIN CURRENT BIAS

CONSTANT GATE VOLTAGE BIAS

Figure 61. Output Power vs. Input Power, VDD = 5 V, Frequency = 26 GHz,

Constant Drain Current Bias (IDD = 140 mA) and Constant Gate Voltage Bias

–10

–5

INPUT POWER (dBm)

CONSTANT DRAIN CURRENT BIAS

CONSTANT GATE VOLTAGE BIAS

Figure 62. PAE vs. Input Power, VDD = 5 V, Frequency = 26 GHz,

Constant Drain Current Bias (IDD = 140 mA) and Constant Gate Voltage Bias

FREQUENCY (GHz)

CONSTANT DRAIN CURRENT BIAS

CONSTANT GATE VOLTAGE BIAS

Figure 63. OP1dB vs. Frequency, VDD =5 V, Constant Drain Current Bias (IDD =

140 mA) and Constant Gate Voltage Bias

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